Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Fair Value Adjustment, by Type [Axis] Fair Value Adjustment, by Type [Axis] Will be used to distinguish between the different reasons for the change in the fair value of an asset or liability. Examples include, foreign exchange, Change in Assumptions, etc. Fair Value Adjustment, by Type [Domain] Fair Value Adjustment, by Type [Domain] [Domain] for Will be used to distinguish between the different reasons for the change in the fair value of an asset or liability. Examples include, foreign exchange, Change in Assumptions, etc. Change in Input Assumptions [Member] Change in Input Assumptions [Member] Represents changes in the fair value of an asset or liability resulting from changes in the inputs used to determine the fair value of the asset or liability. Other changes in Fair Value [Member] Other changes in Fair Value [Member] Represents changes in the fair value of assets or liabilities caused by changes in exchange rates, accretion and other miscellaneous adjustments Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] RARE Management Team [Member] RARE Management Team [Member] After the acquisition of RARE Infrastructure the RARE Management Team will maintain a noncontrolling interest in the company. Outside Investors Outside Investors [Member] This is a group of external companies that are non-controlling partners of, and have retained an ownership in, RARE Infrastructure, an affiliate of Legg Mason, Inc RARE Infrastructure, Ltd [Member] RARE Infrastructure, Ltd [Member] Related to information related specifically to our affiliate, RARE Infrastructure Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Business Acquisition [Line Items] Business Acquisition [Line Items] Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability Assets Under Management Assets under Management, Carrying Amount Noncontrolling Interest, Ownership Percentage by Parent Noncontrolling Interest, Ownership Percentage by Parent Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Payments to Acquire Businesses, Gross Payments to Acquire Businesses, Gross Line of Credit Facility, Fair Value of Amount Outstanding Line of Credit Facility, Fair Value of Amount Outstanding Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Business Combination, Contingent Consideration, Liability Business Combination, Contingent Consideration, Liability Contingent consideration fair value adjustments Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Business Combination, Contingent Consideration, Liability, Current Business Combination, Contingent Consideration, Liability, Current Business Combination, Contingent Consideration, Liability, Noncurrent Business Combination, Contingent Consideration, Liability, Noncurrent Revenues Revenues Accounting Policies [Abstract] Equity [Abstract] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect AOCI Including Portion Attributable to Noncontrolling Interest, before Tax AOCI Including Portion Attributable to Noncontrolling Interest, before Tax Fair Value Disclosures [Abstract] Fair Values of Assets and Liabilities Fair Value Disclosures [Text Block] Variable Interest Entities and Consolidation of Investment Vehicles [Abstract] Variable Interest Entities and Consolidation of Investment Vehicles [Abstract] Consolidated Investment Vehicles and Other Variable Interest Entities Disclosure [Text Block] Variable Interest Entity Disclosure [Text Block] Text Block [Abstract] Schedule of Income Tax Expense [Table] Schedule of Income Tax Expense [Table] A Schedule identifying the components of Income Tax Expense (Benefit) by Federal Foreign and State/Local as well as by Current and Deferred. Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast [Member] Scenario, Forecast [Member] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Domestic Tax Authority [Member] Domestic Tax Authority [Member] State and Local Jurisdiction [Member] State and Local Jurisdiction [Member] Foreign Tax Authority [Member] Foreign Tax Authority [Member] Schedule of Income Tax Expense [Line Items] Schedule of Income Tax Expense [Line Items] [Line Items] for A Schedule identifying the components of Income Tax Expense (Benefit) by Federal Foreign and State/Local as well as by Current and Deferred. Proceeds and Excess Tax Benefit from Share-based Compensation Proceeds and Excess Tax Benefit from Share-based Compensation Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Percent Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Percent Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Percent Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Percent Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Amount Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Amount Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Current Income Tax Expense (Benefit) Current Income Tax Expense (Benefit) Effective Income Tax Rate Reconciliation, Tax Settlement, Percent Effective Income Tax Rate Reconciliation, Tax Settlement, Percent Debt Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] US Treasury Interest Rate [Member] US Treasury Interest Rate [Member] Interest rate at which a bank borrows funds from other banks in the United States interbank market. Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Other Income [Member] Other Income [Member] Other Expense [Member] Other Expense [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 2.7% Senior Notes [Member] 2.7% Senior Notes [Member] 2.7% Senior Notes Due July 2019 [Member] 3.95% Senior Notes [Member] 3.95% Senior Notes [Member] 3.95% Senior Notes due July 2024 [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Swap [Member] Interest Rate Swap [Member] Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] Represents amounts prior to consolidation of consolidated investment entities and eliminations. Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Class of Warrant or Right, Number of Securities Called by Warrants or Rights Class of Warrant or Right, Number of Securities Called by Warrants or Rights Debt Instrument, Unamortized Discount Debt Instrument, Unamortized Discount Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Derivative, Loss on Derivative Derivative, Loss on Derivative Derivative, Notional Amount Derivative, Notional Amount Derivative, Gain on Derivative Derivative, Gain on Derivative Amortization of Deferred Hedge Gains Amortization of Deferred Hedge Gains Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss) Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss) Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Schedule of Changes in Projected Benefit Obligations [Table Text Block] Schedule of Changes in Projected Benefit Obligations [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Schedule of Defined Benefit Plans Disclosures [Table Text Block] Schedule of Defined Benefit Plans Disclosures [Table Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table Text Block] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table Text Block] Long-term Debt, by Current and Noncurrent [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] 4.75% Senior Notes [Member] 4.75% Senior Notes [Member] 4.75% Senior Notes [Member] 5.45% Junior Subordinated Notes [Member] 5.45% Junior Subordinated Notes [Member] 5.45% Junior Subordinated Notes issued in August 2016 due in August 2056 [Member] 5.625% Senior Notes [Member] 5.625% Senior Notes [Member] [Member] 5.625% Senior Notes [Member] 6.375% Junior Notes [Member] 6.375% Junior Notes [Member] 6.375% Junior Notes [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Long-term Debt, Gross Long-term Debt, Gross Long-term Debt Long-term Debt Debt Instrument, Fair Value Disclosure Debt Instrument, Fair Value Disclosure Debt Instrument, Unamortized Discount (Premium), Net Debt Instrument, Unamortized Discount (Premium), Net Debt Instrument, Unamortized Premium Debt Instrument, Unamortized Premium Unamortized Debt Issuance Expense Unamortized Debt Issuance Expense Property, Plant and Equipment [Abstract] Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment by Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Equipment Equipment [Member] Software Software and Software Development Costs [Member] Leasehold improvements Leaseholds and Leasehold Improvements [Member] Property, Plant and Equipment Property, Plant and Equipment [Line Items] Fixed assets: Property, Plant and Equipment, Net, by Type [Abstract] Total cost Property, Plant and Equipment, Gross Less: accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Fixed assets, net Property, Plant and Equipment, Net Contingent Liability Reserve Estimate, Policy [Policy Text Block] Contingent Liability Reserve Estimate, Policy [Policy Text Block] Revenue Recognition, Deferred Revenue [Policy Text Block] Revenue Recognition, Deferred Revenue [Policy Text Block] Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] EnTrustPermal [Member] EnTrustPermal [Member] New affiliate created from the acquisition of EnTrust and merging Permal into it to create a newly branded affiliate, EnTrustPermal. Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Cash and Cash Equivalents [Abstract] Earnings Per Share [Abstract] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Retirement Benefits [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Retirement Plan Tax Status [Axis] Retirement Plan Tax Status [Axis] Retirement Plan Tax Status [Domain] Retirement Plan Tax Status [Domain] Retirement Plan Funding Status [Axis] Retirement Plan Funding Status [Axis] Retirement Plan Funding Status [Domain] Retirement Plan Funding Status [Domain] Retirement Plan Name [Axis] Retirement Plan Name [Axis] Retirement Plan Name [Domain] Retirement Plan Name [Domain] Defined Benefit Plan, Asset Categories [Axis] Defined Benefit Plan, Asset Categories [Axis] Plan Asset Categories [Domain] Plan Asset Categories [Domain] Industry Sector [Axis] Industry Sector [Axis] Industry Sector [Domain] Industry Sector [Domain] Equity Securities by Entity Size [Axis] Equity Securities by Entity Size [Axis] Equity Securities, Entity Size [Domain] Equity Securities, Entity Size [Domain] Equity Securities by Investment Objective [Axis] Equity Securities by Investment Objective [Axis] Equity Securities, Investment Objective [Domain] Equity Securities, Investment Objective [Domain] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Defined Contribution Plan, Employer Discretionary Contribution Amount Defined Contribution Plan, Employer Discretionary Contribution Amount Defined Contribution Plan, Employer Matching Contribution, Percent of Match Defined Contribution Plan, Employer Matching Contribution, Percent of Match Noncontrolling Interest [Abstract] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Other Affiliates [Member] Other Affiliates [Member] Clarion Partners [Member] Clarion Partners [Member] Clarion Partners is a newly acquired company that will be a stand alone affiliate once integrated into Legg Mason. Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Noncontrolling Interest [Member] Noncontrolling Interest [Member] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Proceeds from (Payments to) Noncontrolling Interests Proceeds from (Payments to) Noncontrolling Interests Redeemable Noncontrolling Interest, Equity, Carrying Amount Redeemable Noncontrolling Interest, Equity, Carrying Amount Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange The impact of foreign exchange on the balance of noncontrolling interest holders Noncontrolling Interest, Change in Redemption Value Noncontrolling Interest, Change in Redemption Value Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Dispositions [Abstract] Dispositions [Abstract] Proceeds from Sales of Business, Affiliate and Productive Assets Proceeds from Sales of Business, Affiliate and Productive Assets Share-based Compensation [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Date [Axis] Award Date [Axis] Award Date [Domain] Award Date [Domain] Exercise Price Range [Axis] Exercise Price Range [Axis] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Range of exercise price, 14.81 - 25.00 [Member] [Member] Range of exercise price, 14.81 - 25.00 [Member] [Member] Range of exercise price of LM Stock options of 14.81 - 25.00 [Member] Range of exercise price, 25.01 - 35.00 [Member] Range of exercise price, 25.01 - 35.00 [Member] Represents the range of exercise price in dollars per share from $ 25.01 to 35.00 for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards. Range of exercise price, 35.01 - 55.18 [Member] Range of exercise price, 35.01 - 55.18 [Member] Represents the range of exercise price in dollars per share from $35.01 to $55.18 for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards. Range of exercise price, 35.01 - 94.00 [Member] Range of exercise price, 35.01 - 94.00 [Member] Represents the range of exercise price in dollars per share from $ 35.01 to 94.00 for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards. Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Employee Stock Option Employee Stock Option [Member] Stock based compensation disclosure Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Income Tax Disclosure [Abstract] Valuation Allowance [Table] Valuation Allowance [Table] Prospective Adoption of New Accounting Pronouncements [Axis] Prospective Adoption of New Accounting Pronouncements [Axis] Accounting Guidance [Domain] Accounting Guidance [Domain] Deferred Compensation, Share-based Payments [Member] Deferred Compensation, Share-based Payments [Member] Other Deferred Tax Asset, by Type [Axis] Other Deferred Tax Asset, by Type [Axis] Identifies the types of other deferred tax assets disclosed in the calculation in deferred tax assets Other Deferred Tax Asset, by Type [Domain] Other Deferred Tax Asset, by Type [Domain] [Domain] for Identifies the types of other deferred tax assets disclosed in the calculation in deferred tax assets UNITED STATES UNITED STATES Valuation Allowance by Deferred Tax Asset [Axis] Valuation Allowance by Deferred Tax Asset [Axis] Deferred Tax Asset [Domain] Deferred Tax Asset [Domain] Valuation Allowance, Operating Loss Carryforwards [Member] Valuation Allowance, Operating Loss Carryforwards [Member] Valuation Allowance, Tax Credit Carryforward [Member] Valuation Allowance, Tax Credit Carryforward [Member] Contribution of Monetary Assets by an Enterprise to a Charitable Organization [Domain] Contribution of Monetary Assets by an Enterprise to a Charitable Organization [Domain] Amount of valuation allowances attributable to deductible charitable contribution carryforwards. Valuation Allowance of Deferred Tax Assets [Member] Valuation Allowance of Deferred Tax Assets [Member] Valuation Allowance, Other Tax Carryforward [Member] Valuation Allowance, Other Tax Carryforward [Member] Valuation Allowance [Line Items] Valuation Allowance [Line Items] Deferred Tax Assets, Operating Loss Carryforwards Deferred Tax Assets, Operating Loss Carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Foreign Deferred Tax Assets, Operating Loss Carryforwards, Foreign Deferred Tax Assets, Valuation Allowance Deferred Tax Assets, Valuation Allowance Tax Credit Carryforward, Valuation Allowance Tax Credit Carryforward, Valuation Allowance Operating Loss Carryforwards, Valuation Allowance Operating Loss Carryforwards, Valuation Allowance Deferred Tax Assets, Operating Loss Carryforwards, Domestic Deferred Tax Assets, Operating Loss Carryforwards, Domestic Deferred Tax Assets, Capital Loss Carryforwards Deferred Tax Assets, Capital Loss Carryforwards Deferred Tax Assets, Tax Credit Carryforwards Deferred Tax Assets, Tax Credit Carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration Deferred Tax Assets, Charitable Contribution Carryforwards Deferred Tax Assets, Charitable Contribution Carryforwards Deferred Tax Assets, Operating Loss Carryforwards, State and Local Deferred Tax Assets, Operating Loss Carryforwards, State and Local Document Information [Abstract] Document Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float QS Investors [Domain] QS Investors [Domain] QS Investors [Domain] Contingent Consideration by Type [Axis] Contingent Consideration by Type [Axis] Contingent Consideration Type [Domain] Contingent Consideration Type [Domain] Contingent payment due on second anniversary of acquisition Contingent payment due on second anniversary of acquisition [Member] Contingent payment due on second anniversary of acquisition. Contingent payment due on fourth anniversary of acquisition [Member] Contingent payment due on fourth anniversary of acquisition [Member] Contingent payment due on fourth anniversary of acquisition. Martin Currie [Member] Martin Currie [Member] An affiliate, Martin Currie, that is a leading international equity specialist based in Edinburgh, Scotland. Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Business Acquisition, Preacquisition Contingency, Amount of Settlement Business Acquisition, Preacquisition Contingency, Amount of Settlement Non-employee directors [Abstract] Non-employee directors [Abstract] Restricted Stock [Member] Restricted Stock [Member] Common Stock [Member] Common Stock [Member] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Director [Member] Director [Member] Share-based Compensation Arrangement by Share-based Payment Award Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized ShareBasedCompensationArrangementbyShare-basedPaymentAwardSharesIssued ShareBasedCompensationArrangementbyShare-basedPaymentAwardSharesIssued Number of Shares Issued Under Equity Plan Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value Compensation and Employee Benefit Plans [Text Block] Compensation and Employee Benefit Plans [Text Block] Components of fixed assets Property, Plant and Equipment [Table Text Block] Earnings Per Share [Text Block] Earnings Per Share [Text Block] Accumulated Other Comprehensive Income [Abstract] Accumulated Other Comprehensive Income [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Statement of Cash Flows [Abstract] Statement [Table] Statement [Table] 5.5% Senior Notes [Member] 5.5% Senior Notes [Member] 5.5% Senior Notes Management Equity Plan [Member] Management Equity Plan [Member] A plan that allows the key employees of an affiliate to participate in the future growth of the enterprise value subsequent to the date of grant. Consolidated Investment Vehicles [Member] Consolidated Investment Vehicles [Member] Voting Interest Entities and Voting Rights Entities that are consolidated into the financial statements of the registrant. The specific variable interest entities controlled by the entity may be included as children of this element. Although the registrant may not control the VIE through voting interests, it has a variable interest that will absorb a majority of the entity's expected losses, receive a majority of the entity's expected residual returns, or both. In general, a VIE is a corporation, partnership, trust, or any other legal structure used for business purposes that either (a) does not have equity investors with voting rights or (b) has equity investors that do not provide sufficient financial resources for the entity to support its activities. A VIE often holds financial assets, including loans or receivables, real estate or other property. A VIE may be essentially passive or it may engage in research and development or other activities on behalf of another company. Consolidated Legg Mason, Inc. Consolidated Legg Mason [Domain] The consolidated financial information of the entity, including the portion which relates to consolidated variable interest entities. Statement [Line Items] Statement [Line Items] Income Taxes Paid, Net Income Taxes Paid, Net CASH FLOWS FROM OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Payment for Debt Extinguishment or Debt Prepayment Cost Payment for Debt Extinguishment or Debt Prepayment Cost Adjustments to reconcile Net Income to net cash used in operations: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Depreciation and amortization Depreciation and Amortization Excluding Amortization of Deferred Sales Commissions The aggregate amount of depreciation expense and amortization expense. Depreciation expense is the noncash expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Amortization expense is the noncash expense charged against earnings in the current period that reflects the allocation of the cost of definite lived intangible assets and leasehold improvements over the shorter of their estimated remaining economic lives or the lease term. Excludes the amortization of deferred sales commissions. Accretion and amortization of securities discounts and premiums, net Accretion (Amortization) of Discounts and Premiums, Investments Stock-based compensation Share-based Compensation Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense Deferred Compensation Arrangement with Individual, Compensation Expense Deferred Compensation Arrangement with Individual, Compensation Expense Unrealized Gain (Loss) on Investments Unrealized Gain (Loss) on Investments Net (gains) losses on investments Gain (Loss) on Investments Deferred income taxes Deferred Income Tax Expense (Benefit) Other Other Noncash Income (Expense) Decrease (increase) in assets: Increase (Decrease) in Operating Assets [Abstract] Investment advisory and related fees receivable Increase (Decrease) in Accounts Receivable Net (purchases) sales of trading and other current investments Proceeds from (Payments for) Trading Securities, Short-term Other receivables Increase (Decrease) in Other Receivables Other assets Increase (Decrease) in Other Operating Assets Increase (decrease) in liabilities: Increase (Decrease) in Operating Liabilities [Abstract] Accrued compensation Increase (Decrease) in Employee Related Liabilities Deferred compensation Increase (Decrease) in Deferred Compensation Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Other liabilities Increase (Decrease) in Other Operating Liabilities CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities, Continuing Operations CASH FLOWS FROM INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Payments for fixed assets Payments to Acquire Property, Plant, and Equipment Business acquisitions, net of cash acquired of $29,830 Payments to Acquire Businesses, Net of Cash Acquired Payments to Acquire Assets, Investing Activities Payments to Acquire Assets, Investing Activities Proceeds from Sales of Assets, Investing Activities Proceeds from Sales of Assets, Investing Activities Contingent Payment Received, Investing Activities Contingent Payment Received, Investing Activities A payment received in connection with a prior sale of a business based on meeting certain contingencies Cash Acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Change in restricted cash Increase (Decrease) in Restricted Cash Proceeds from sales and maturities of investment securities Proceeds from Sale and Maturity of Marketable Securities CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from Lines of Credit Proceeds from Lines of Credit Debt issuance costs Payments of Debt Issuance Costs Payment for Contingent Consideration Liability, Financing Activities Payment for Contingent Consideration Liability, Financing Activities Business Acquisition, Preacquisition Contingency, Amount of Settlement Payment for Contingent Consideration Liability, Operating Activities Issuance of common stock for stock-based compensation Proceeds from Issuance of Common Stock Proceeds from Issuance of Long-term Debt Proceeds from Issuance of Long-term Debt Employee Tax Withholdings by settlement of net share transaction Employee Tax Withholdings Related to net share transaction Employee Tax Withholdings Related to net share transactions Repurchase of common stock Payments for Repurchase of Common Stock Dividends paid Payments of Dividends Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities EFFECT OF EXCHANGE RATES ON CASH Effect of Exchange Rate on Cash and Cash Equivalents NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, Period Increase (Decrease) CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR Cash and Cash Equivalents, at Carrying Value CASH AND CASH EQUIVALENTS AT END OF YEAR Interest Paid Interest Paid Proceeds from Income Tax Refunds Proceeds from Income Tax Refunds Statement of Stockholders' Equity [Abstract] EnTrust Capital [Member] EnTrust Capital [Member] Newly acquired affiliate that will immediately become EnTrustPermal. Royce [Member] Royce [Member] Royce is a wholly owned affiliate of Legg Mason, that invests primarily in Small Cap Companies. COMMON STOCK ADDITIONAL PAID-IN CAPITAL Additional Paid-in Capital [Member] EMPLOYEE STOCK TRUST Employee Stock Trust [Member] Common stock issued to a trust (for example, a 'rabbi trust') set up specifically to accumulate stock for the sole purpose of distribution to participating employees. This trust does not allow employees to immediately or after a holding period diversify into nonemployer securities. The deferred compensation plan for which this trust is set up must be settled by the delivery of a fixed number of shares of employer stock. DEFERRED COMPENSATION EMPLOYEE STOCK TRUST Deferred Compensation Employee Stock Trust [Member] Common stock issued to a deferred compensation employee stock trust, which is set up specifically to accumulate stock for the sole purpose of distribution to participating employees. This trust does not allow employees to immediately or after a holding period diversify into nonemployer securities. The deferred compensation plan for which this trust is set up must be settled by the delivery of a fixed number of shares of employer stock. RETAINED EARNINGS Retained Earnings [Member] ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), NET AOCI Attributable to Parent [Member] Common Stock, Other Value, Outstanding Common Stock, Other Value, Outstanding Capital Common Stock, Shares Authorized Preferred Stock, Shares Outstanding Preferred Stock, Shares Outstanding Common Stock, Capital Shares Reserved for Future Issuance Common Stock, Capital Shares Reserved for Future Issuance Stock Repurchase Program, Remaining Authorized Repurchase Amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Stock Repurchase Program, Authorized Amount Stock Repurchase Program, Authorized Amount Stock Repurchased and Retired During Period, Shares Stock Repurchased and Retired During Period, Shares Shares Paid for Tax Withholding for Share Based Compensation Shares Paid for Tax Withholding for Share Based Compensation Stockholders' Equity Attributable to Parent Stockholders' Equity Attributable to Parent Stockholders' Equity Attributable to Noncontrolling Interest Stockholders' Equity Attributable to Noncontrolling Interest Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest Beginning Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Stock options exercised Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options Deferred compensation employee stock trust Deferred Compensation Employee Stock Trust, Stockholders Equity Impact Aggregate change in value for phantom 401k transactions during the period. Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Stock-based compensation Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Adjustments to Additional Paid in Capital, Other Adjustments to Additional Paid in Capital, Other Employee tax withholdings by settlement of net share transactions Adjustments Related to Tax Withholding for Share-based Compensation Shares repurchased and retired Stock Repurchased and Retired During Period, Value APIC reclassified for MEP vesting APIC reclassified for MEP vesting Additional paid-in capital reclassified for management equity plan vesting Allocation from Convertible Senior Notes Net of Tax Allocation from Convertible Senior Notes Net of Tax Allocation from the repurchase of the 2.5% Convertible Senior Notes, Net of Tax, as displayed in the statement of changes in stockholders' equity Shares Issued to plans Shares Issued to Employee Stock Trust Plans Aggregate change in value for stock issued during the period as a result of employee stock trust plans. Distributions and forfeitures Distributions and Forfeitures to Employee Stock Trust Plans Value of stock related to Employee Stock Trust Plans that was distributed and forfeited during the period. Net Income Attributable to Legg Mason, Inc. Net Income (Loss) Attributable to Parent Dividends declared Dividends RE Reclassified for MEP Amortization RE Reclassified for MEP Amortization This is the accretion on the MEP plans and it is reclassified out of retained earnings and into Noncontrolling Interests throughout the quarter Excess Tax Benefit from Share-based Compensation, Financing Activities Excess Tax Benefit from Share-based Compensation, Financing Activities Reclassification from Retained Earnings to Noncontrolling Interests Reclassification from Retained Earnings to Noncontrolling Interests The proper accounting for some of our equity arrangements with affiliates as well as other activity requires a reclassification from retained earnings into noncontrolling interests in order to appropriately maintain the fair value of or record accretion related to noncontrolling interests Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax Ending Balance Stock Issued During Period, Value, Stock Options Exercised Stock Issued During Period, Value, Stock Options Exercised Common Stock Issued, Employee Stock Trust Common Stock Issued, Employee Stock Trust Employee Tax Withholdings Related to net share transaction Common Stock, Dividends, Per Share, Declared Common Stock, Dividends, Per Share, Declared Long-Term Debt Debt Disclosure [Text Block] Net Income (Loss) Attributable to Noncontrolling Interest Net Income (Loss) Attributable to Noncontrolling Interest Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Schedule of Goodwill by Book Value [Axis] Schedule of Goodwill by Book Value [Axis] This element represents the disclosures required for goodwill, including gross value, accumulated impairment and net book value. Goodwill by Book Value [Domain] Goodwill by Book Value [Domain] This element represents the disclosures required for the purpose of calculating net book value of goodwill. Goodwill Gross Value [Member] Goodwill Gross Value [Member] This element represents the gross book value of the goodwill. Goodwill Accumulated Impairment [Member] Goodwill Accumulated Impairment [Member] This element represents the accumulated loss recognized from the impairment of goodwill. Goodwill Net Value [Member] Goodwill Net Value [Member] This element represents the net book value of the goodwill. Goodwill Goodwill [Line Items] Goodwill, Gross Goodwill, Gross Goodwill, Acquired During Period Goodwill, Acquired During Period Other Intangible Assets, Net Other Intangible Assets, Net Goodwill, Impaired, Accumulated Impairment Loss Goodwill, Impaired, Accumulated Impairment Loss Goodwill Goodwill Impact of excess tax basis amortization Goodwill, Subsequent Recognition of Deferred Tax Asset Business Acquisition, Goodwill, Expected Tax Deductible Amount Business Acquisition, Goodwill, Expected Tax Deductible Amount Other, including changes in foreign exchange rates Goodwill, Other Increase (Decrease) Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Bonds [Member] Bonds [Member] Cash [Member] Cash [Member] Equity [Member] Equity [Member] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss) Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss) Defined Benefit Plan, Benefit Obligation, Business Combination Defined Benefit Plan, Benefit Obligation, Business Combination Defined Benefit Plan, Benefit Obligation, Benefits Paid Defined Benefit Plan, Benefit Obligation, Benefits Paid Defined Benefit Plan, Interest Cost Defined Benefit Plan, Interest Cost Defined Benefit Plan, Plan Assets, Benefits Paid Defined Benefit Plan, Plan Assets, Benefits Paid Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) Defined Benefit Plan, Plan Assets, Contributions by Employer Defined Benefit Plan, Plan Assets, Contributions by Employer Defined Benefit Plan, Expected Return (Loss) on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Fair Value of Plan Assets Defined Benefit Plan, Fair Value of Plan Assets Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Defined Benefit Plan, Actual Plan Asset Allocations Defined Benefit Plan, Actual Plan Asset Allocations Defined Benefit Plan, Target Allocation Percentage Defined Benefit Plan, Target Allocation Percentage Defined Benefit Plan, Benefit Obligation Defined Benefit Plan, Benefit Obligation Defined Benefit Plan, Funded (Unfunded) Status of Plan Defined Benefit Plan, Funded (Unfunded) Status of Plan Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months Defined Benefit Plan, Expected Future Benefit Payment, Year Two Defined Benefit Plan, Expected Future Benefit Payment, Year Two Defined Benefit Plan, Expected Future Benefit Payment, Year Three Defined Benefit Plan, Expected Future Benefit Payment, Year Three Defined Benefit Plan, Expected Future Benefit Payment, Year Four Defined Benefit Plan, Expected Future Benefit Payment, Year Four Defined Benefit Plan, Expected Future Benefit Payment, Year Five Defined Benefit Plan, Expected Future Benefit Payment, Year Five Defined Benefit Plan, Plan Assets, Contributions by Employer Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year, Description Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureEmployerContributionFinal DefinedBenefitPlanExpectedFutureEmployerContributionFinal Defined Benefit Plan Expected Future Employer Contribution Final Schedule of Variable Interest Entities [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Consolidation, Eliminations [Member] Consolidation, Eliminations [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Consolidated Entity Excluding Variable Interest Entities (VIE) [Member] Consolidated Entity Excluding Variable Interest Entities (VIE) [Member] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity Variable Interest Entity [Line Items] Current Assets Assets, Current Non-current Assets Assets, Noncurrent TOTAL ASSETS Assets Current Liabilities Liabilities, Current Non-current Liabilities Liabilities, Noncurrent TOTAL LIABILITIES Liabilities REDEEMABLE NONCONTROLLING INTERESTS Total Stockholders' Equity TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Restricted stock and restricted stock unit transactions Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Scheduleof Deferred Tax Assets and Liabilities [Abstract] Scheduleof Deferred Tax Assets and Liabilities [Abstract] Schedule of Deferred Tax Assets [Table] Schedule of Deferred Tax Assets [Table] A Schedule outlining the components of deferred tax assets and deferred tax liabilities Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] PENNSYLVANIA PENNSYLVANIA Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Subsidiaries [Member] Subsidiaries [Member] Permal [Member] Permal [Member] Represents the acquired business of Permal. Federal Benefit of Uncertain Tax Positions [Member] Federal Benefit of Uncertain Tax Positions [Member] Identifies the amount of deferred tax assets arising from uncertain tax positions Fund Launch Costs [Member] Fund Launch Costs [Member] Identifies the amount of deferred tax assets arising from costs to launch new funds Pension Plan [Member] Pension Plan [Member] Schedule of Deferred Tax Assets [Line Items] Schedule of Deferred Tax Assets [Line Items] [Line Items] for A Schedule outlining the components of deferred tax assets and deferred tax liabilities Increase (Decrease) in Deferred Income Taxes Increase (Decrease) in Deferred Income Taxes Increase (Decrease) in Deferred Liabilities Increase (Decrease) in Deferred Liabilities Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities Deferred Tax Assets, Tax Credit Carryforwards, Foreign Deferred Tax Assets, Tax Credit Carryforwards, Foreign Deferred Tax Assets, Other Deferred Tax Assets, Other Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions Deferred Tax Assets, Gross Deferred Tax Assets, Gross Deferred Tax Assets, Valuation Allowance Deferred Tax Assets, Net of Valuation Allowance Deferred Tax Assets, Net of Valuation Allowance Deferred Tax Assets, Net Deferred Tax Assets, Net Deferred Tax Liabilities, Goodwill and Intangible Assets Deferred Tax Liabilities, Goodwill and Intangible Assets Deferred Tax Liabilities, Property, Plant and Equipment Deferred Tax Liabilities, Property, Plant and Equipment Deferred Tax Liabilities, Unrealized Gains on Trading Securities Deferred Tax Liabilities, Unrealized Gains on Trading Securities Deferred Tax Liabilities, Investments Deferred Tax Liabilities, Investments Deferred Tax Liabilities, Other Deferred Tax Liabilities, Other Deferred Tax Liabilities, Gross Deferred Tax Liabilities, Gross Deferred Tax Liabilities, Net Deferred Tax Liabilities, Net U.S. Earnings U.S. Earnings Represents the amount of expected future US Earnings required to realized expected Deferred Tax Assets. The estimated amount is as of the balance sheet date Foreign Earnings Foreign Earnings Represents the amount of expected future foreign earnings required to realized expected deferred tax assets. The estimated amount is as of the balance sheet date. Valuation Allowances and Reserves, Balance Valuation Allowances and Reserves, Balance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Commitments and Contingencies Disclosure [Abstract] Other Commitments [Table] Other Commitments [Table] Financial Guard LLC [Member] Financial Guard LLC [Member] Financial Guard LLC is an online registered investment advisor and innovative technology-enabled wealth management and investment advice platform company acquired by Legg Mason Inc [Member] Other Commitments [Axis] Other Commitments [Axis] Other Commitments [Domain] Other Commitments [Domain] Investment In Limited Partnerships [Member] Investment In Limited Partnerships [Member] The amount committed to invest in limited partnerships that make private investments. Proprietary Funds [Member] Proprietary Funds [Member] Investments in Proprietary Funds Other Commitments [Line Items] Other Commitments [Line Items] Other Commitment Other Commitment Other Commitment, Amount Paid Other Commitment, Amount Paid Represents the amount of a previously disclosed other commitment that has already been paid. Capital Stock [Abstract] Capital Stock [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Line Items] Class of Stock [Line Items] Schedule of Stock by Class [Table Text Block] Schedule of Stock by Class [Table Text Block] Property, Plant and Equipment [Table] Depreciation and amortization Depreciation, Depletion and Amortization Accelerated Depreciation, Other Accelerated Depreciation, Other Amount of accelerated depreciation charged against earnings that is for purposes other than restructuring. Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Schedule of Variable Interest Entities [Table] Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount Mergers, Acquisitions and Dispositions Disclosures [Text Block] Mergers, Acquisitions and Dispositions Disclosures [Text Block] Basis of Accounting, Policy [Policy Text Block] Basis of Accounting, Policy [Policy Text Block] Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table] Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table] Weighted Average [Member] Weighted Average [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fund management contracts Fund management contracts [Member] Represents fund management contracts member. Contingent Consideration Liability Contingent consideration liability [Member] Contingent consideration liability [Member] Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] Fair Value Inputs, Attrition Rate Fair Value Inputs, Attrition Rate Amount used to represent the attrition when calculating the fair value of amortizable asset management contracts Fair Value Inputs, Discount Rate Fair Value Inputs, Discount Rate Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Fair Value Inputs, Long-term Revenue Growth Rate Fair Value Inputs, Long-term Revenue Growth Rate Reconciliation of Tax Rate [Table] Reconciliation of Tax Rate [Table] Schedule reconcilling the difference between the federal tax rate and the effective tax rate Federal State and Local [Member] Federal State and Local [Member] Federal State and Local [Member] UNITED KINGDOM UNITED KINGDOM NEW YORK NEW YORK Reconciliation of Tax Rate [Line Items] Reconciliation of Tax Rate [Line Items] [Line Items] for Schedule reconcilling the difference between the federal tax rate and the effective tax rate Tax Benefit, Impairment of Intangible Assets, Indefinite Lived (Excluding Goodwill) Tax Benefit, Impairment of Intangible Assets, Indefinite Lived (Excluding Goodwill) Tax Benefit, Impairment of Intangible Assets, Indefinite Lived (Excluding Goodwill) Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Noncontrolling Interest Disclosure [Text Block] Noncontrolling Interest Disclosure [Text Block] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Treasury Lock [Member] Treasury Lock [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items] Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Derivative [Table] Derivative [Table] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Underlying Asset Class [Domain] Underlying Asset Class [Domain] Derivative Financial Instruments, Assets [Member] Derivative Financial Instruments, Assets [Member] Total Return Swap [Member] Total Return Swap [Member] Future [Member] Future [Member] Derivative Derivative [Line Items] Aggregate Counterparty Investment in ETF Aggregate Counterparty Investment in ETF Represents the initial amount invested into a Legg Mason sponsored ETF by a third-party investor Statement of Comprehensive Income [Abstract] Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Subsequent Event [Abstract] Subsequent Event [Abstract] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Derivative Assets at Fair Value [Table Text Block] Schedule of Derivative Assets at Fair Value [Table Text Block] Schedule of Derivative Liabilities at Fair Value [Table Text Block] Schedule of Derivative Liabilities at Fair Value [Table Text Block] Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance Derivative Instruments, Gain (Loss) [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] 2.5% Convertible Senior Notes [Member] 2.5% Convertible Senior Notes [Member] 2.5% Convertible Senior Notes [Member] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Antidilutive shares due to proceeds from exercising exceeded price of shares [Domain] Antidilutive shares due to proceeds from exercising exceeded price of shares [Domain] Antidilutive shares due to proceeds from exercising exceeded price of shares [Domain] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Investment, Policy [Policy Text Block] Investment, Policy [Policy Text Block] Investment Income [Table Text Block] Investment Income [Table Text Block] Investments [Member] Investments [Member] Not Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument [Member] Foreign Exchange Forward [Member] Foreign Exchange Forward [Member] Forward Contracts [Member] Forward Contracts [Member] Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Liability Derivative Asset, Fair Value, Gross Liability Derivative Asset Derivative Asset Derivative Asset, Not Subject to Master Netting Arrangement Derivative Asset, Not Subject to Master Netting Arrangement Derivative Asset, Collateral, Obligation to Return Cash, Offset Derivative Asset, Collateral, Obligation to Return Cash, Offset Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement Income Statement [Abstract] Nature of Expense [Axis] Nature of Expense [Axis] Interim Period, Costs Not Allocable [Domain] Interim Period, Costs Not Allocable [Domain] Restructuring Charges [Member] Restructuring Charges [Member] Separate Accounts [Member] Separate Accounts [Member] A member of the Investment Type axis to segregate out the portion of assets, revenue, etc that is related to Separate Accounts Mutual Funds [Member] Mutual Funds [Member] This is a member of the Investment Type axis and is used to segregate out the portion of assets, revenues, etc related to Mutuals Funds Performance Fees [Member] Performance Fees [Member] Market Input used to calculate the fair value of the contingent consideration. OPERATING REVENUES Revenues [Abstract] Investment Advisory Fees Investment Advisory Fees Distribution and service fees Distribution and Servicing Fees Other Revenue, Other Financial Services Revenues OPERATING EXPENSES Costs and Expenses [Abstract] Compensation and benefits Labor and Related Expense Distribution and servicing Noninterest Expense Distribution and Servicing Fees Communications and technology Communications and Information Technology Occupancy Occupancy, Net Amortization of intangible assets Amortization of Intangible Assets Impairment of Intangible Assets Asset Impairment Charges Other Other Expenses Total Operating Expenses Operating Expenses OPERATING INCOME Operating Income (Loss) OTHER NON-OPERATING INCOME (EXPENSE) Nonoperating Income (Expense) [Abstract] Interest income Investment Income, Interest Interest expense Interest Expense Other income (expense), net Other Nonoperating Income (Expense) Total Other Non-Operating Income (Expense) Nonoperating Income (Expense) INCOME BEFORE INCOME TAX PROVISION Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax provision Income Tax Expense (Benefit) NET INCOME NET INCOME ATTRIBUTABLE TO LEGG MASON, INC. NET INCOME PER SHARE ATTRIBUTABLE TO LEGG MASON, INC. COMMON SHAREHOLDERS Basic (in dollars per share) Earnings Per Share, Basic Diluted (in dollars per share) Earnings Per Share, Diluted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Income Tax Disclosure [Text Block] Income Tax Disclosure [Text Block] Variable Interest Entity, Not Primary Beneficiary [Member] Variable Interest Entity, Not Primary Beneficiary [Member] Real Estate Investment Trusts [Member] Real Estate Investment Trusts [Member] Represents Variable Interests in Real Estate Investment Trusts Other sponsored investments fund [Member] Other sponsored investments fund [Member] Represents a significant variable interest entity for which the entity is not the primary beneficiary related to other sponsored investment funds not otherwise specified in the taxonomy. Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Condensed Income Statement [Table] Condensed Income Statement [Table] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Total Operating Expenses OPERATING INCOME INCOME BEFORE INCOME TAX PROVISION NET INCOME Net Income Attributable to Legg Mason, Inc. Debt, Policy [Policy Text Block] Debt, Policy [Policy Text Block] Salaries, Wages and Officers' Compensation [Abstract] Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits, by Title of Individual and by Type of Deferred Compensation [Table] Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits, by Title of Individual and by Type of Deferred Compensation [Table] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] ClearBridge Investments [Member] ClearBridge Investments [Member] ClearBridge Investments [Member] Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items] Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items] Stock Issued During Period, Value, Restricted Stock Award, Gross Stock Issued During Period, Value, Restricted Stock Award, Gross Profits interests equity plan participation percentage Profits interests equity plan participation percentage Represents the percentage of participation in future growth in value of the affiliate available for participation by key employees under the terms of a profits interest management equity plan. Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Aggregate Cost of Awards Aggregate Cost of Awards The aggregate cost of the award is based on individual valuations Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued Statement of Financial Position [Abstract] Currency [Axis] Currency [Axis] All Currencies [Domain] All Currencies [Domain] United Kingdom, Pounds United Kingdom, Pounds Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Rabbi trust [Domain] Rabbi trust [Domain] Rabbi trust Other Segments [Member] Other Segments [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Non-US [Member] Non-US [Member] Trade Names [Member] Trade Names [Member] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Permal funds-of-hedge fund management contracts [Member] Permal funds-of-hedge fund management contracts [Member] Related to the Permal funds-of-hedge fund management contracts Incentive Distribution, Recipient [Domain] Incentive Distribution, Recipient [Domain] Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] A plan where shares of the companies stock are purchased in the open market on behalf of the employees and at the option of the employee to participate in the plan. Employee Stock Option [Member] Long Term Incentive Compensation Plans [Member] Long Term Incentive Compensation Plans [Member] Represents the fair value of long term incentive compensation plans recorded as trading investments ASSETS Assets [Abstract] Current Assets Assets, Current [Abstract] Cash and Cash Equivalents Restricted cash Restricted Cash and Cash Equivalents, Current Receivables: Receivables, Net, Current [Abstract] Investment advisory and related fees Accounts Receivable, Net, Current Other receivables Other Receivables, Net, Current Investment securities Short-term Investments Other current assets Other Assets, Current Total Current Assets Fixed assets, net Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Deferred income taxes Deferred Tax Assets, Net of Valuation Allowance, Noncurrent Other non-current assets Other Assets, Noncurrent TOTAL ASSETS LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] LIABILITIES Liabilities [Abstract] Current Liabilities Liabilities, Current [Abstract] Accrued compensation Employee-related Liabilities, Current Accounts Payable and Accrued Liabilities, Current Accounts Payable and Accrued Liabilities, Current Line of Credit, Current Line of Credit, Current Business Combination, Contingent Consideration, Liability, Current Other current liabilities Other Liabilities, Current Total Current Liabilities Deferred compensation Deferred Compensation Liability, Classified, Noncurrent Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Other non-current liabilities Other Liabilities, Noncurrent Long-term Debt Long-term Debt, Excluding Current Maturities TOTAL LIABILITIES STOCKHOLDERS' EQUITY Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common stock, par value $.10; authorized 500,000,000 shares; issued 84,606,408 shares in March 2018 and 95,726,628 shares in March 2017 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Employee stock trust Deferred compensation employee stock trust Compensation and Benefits Trust Retained earnings Retained Earnings, Unappropriated TOTAL STOCKHOLDERS' EQUITY TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY Common Stock, Par or Stated Value Per Share Common Stock, Par or Stated Value Per Share Common Stock, Shares Authorized Common Stock, Shares, Issued Common Stock, Shares, Issued Deferred Compensation Arrangement with Individual, Shares Authorized for Issuance Deferred Compensation Arrangement with Individual, Shares Authorized for Issuance Discontinued Operations and Disposal Groups [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Litigation Settlement, Expense Litigation Settlement, Expense Loss Contingency Accrual Loss Contingency Accrual Loss Contingency Accrual, Provision Loss Contingency Accrual, Provision Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Line of Credit Facility [Table] Line of Credit Facility [Table] Interest Expense [Member] Interest Expense [Member] Cash Flow Hedging [Member] Cash Flow Hedging [Member] Designated as Hedging Instrument [Member] Designated as Hedging Instrument [Member] Lender Name [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility [Member] Revolving Credit Facility [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Derivative, Fixed Interest Rate Derivative, Fixed Interest Rate Derivative, Term of Contract Derivative, Term of Contract Derivative Liability, Not Subject to Master Netting Arrangement Derivative Liability, Not Subject to Master Netting Arrangement Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Deferred Tax Assets, Hedging Transactions Deferred Tax Assets, Hedging Transactions Derivative, Loss on Derivative Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Variable Interest Entity, Primary Beneficiary [Member] CIVs Private Equity Funds