Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Weighted Average Fair Values and Valuation Assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Stock Options and SARs Transactions Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Restricted Stock and Restricted Stock Unit Transactions Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Weighted Average Fair Values and Valuation Assumptions for Performance Award Grants Performance Units and Performance Stock Grants Weighted Average Fair Values and Valuation Assumptions [Table Text Block] Performance Units and Performance Stock Grants Weighted Average Fair Values and Valuation Assumptions [Table Text Block] Asset Retirement Obligation [Abstract] Carrying Amount at January 1 Asset Retirement Obligation Liabilities Incurred Asset Retirement Obligation, Liabilities Incurred Liabilities Settled (1) Asset Retirement Obligation, Liabilities Settled Accretion Asset Retirement Obligation, Accretion Expense Revisions Asset Retirement Obligation, Revision of Estimate Foreign Currency Translations Asset Retirement Obligation, Foreign Currency Translation Gain (Loss) Carrying Amount at March 31 Current Portion Asset Retirement Obligation, Current Noncurrent Portion Asset Retirement Obligations, Noncurrent Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Statement of Cash Flows [Abstract] Cash Flows from Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net Income Net Income (Loss) Attributable to Parent Items Not Requiring (Providing) Cash Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, Depletion and Amortization Depreciation, Depletion and Amortization Impairments Impairment of Oil and Gas Properties Stock-Based Compensation Expenses Share-based Compensation Deferred Income Taxes Deferred Income Tax Expense (Benefit) Losses on Asset Dispositions, Net Gain (Loss) on Disposition of Assets Other, Net Other Noncash Income (Expense) Mark-to-Market Commodity Derivative Contracts Unrealized Gain (Loss) on Derivatives and Commodity Contracts [Abstract] Total (Gains) Losses Unrealized Gain (Loss) on Derivatives and Commodity Contracts Net Cash Received from (Payments for) Settlements of Commodity Derivative Contracts Realized Gains (Losses) This element reflects realized gain (loss) on the settlement of financial commodity derivative instruments. Other, Net Other, Net Excluding Gains Losses The cash inflows/outflows from operating activities not classfied elsewhere. Changes in Components of Working Capital and Other Assets and Liabilities Increase (Decrease) in Operating Capital [Abstract] Accounts Receivable Increase (Decrease) in Receivables Inventories Increase (Decrease) in Inventories Accounts Payable Increase (Decrease) in Accounts Payable Accrued Taxes Payable Increase (Decrease) in Accrued Taxes Payable Other Assets Increase (Decrease) in Other Operating Assets Other Liabilities Increase (Decrease) in Other Operating Liabilities Changes in Components of Working Capital Associated with Investing and Financing Activities Changes in Components of Working Capital Associated with Investing and Financing Activities The net change during the reporting period of all current assets and liabilities used in investing and financing activities. Net Cash Provided by Operating Activities Net Cash Provided by (Used in) Operating Activities Investing Cash Flows Net Cash Provided by (Used in) Investing Activities [Abstract] Additions to Oil and Gas Properties Payments to Acquire Oil and Gas Property and Equipment Additions to Other Property, Plant and Equipment Payments to Acquire Other Property, Plant, and Equipment Proceeds from Sales of Assets Proceeds from Sale of Oil and Gas Property and Equipment Changes in Components of Working Capital Associated with Investing Activities Changes in Components of Working Capital Associated with Investing Activities The net change during the reporting period of all current assets and liabilities used in investing and financing activities. Net Cash Used in Investing Activities Net Cash Provided by (Used in) Investing Activities Financing Cash Flows Net Cash Provided by (Used in) Financing Activities [Abstract] Dividends Paid Payments of Ordinary Dividends Treasury Stock Purchased Payments for Repurchase of Common Stock Proceeds from Stock Options Exercised and Employee Stock Purchase Plan Proceeds from Stock Options Exercised Repayment of Capital Lease Obligation Repayments of Long-term Capital Lease Obligations Changes in Components of Working Capital Associated with Financing Activities Changes In Components Of Working Capital Associated With Financing Activities The net change during the reporting period of all assets and liabilities used in financing activities. Net Cash Used in Financing Activities Net Cash Provided by (Used in) Financing Activities Effect of Exchange Rate Changes on Cash Effect of Exchange Rate on Cash and Cash Equivalents Decrease in Cash and Cash Equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and Cash Equivalents at Beginning of Period Cash and Cash Equivalents, at Carrying Value Cash and Cash Equivalents at End of Period Capitalized Exploratory Well Costs [Abstract] Net Changes In Capitalized Exploratory Well Costs Capitalized Exploratory Well Costs, Roll Forward [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative [Table] Derivative [Table] Energy [Axis] Energy [Axis] Energy [Domain] Energy [Domain] Crude Oil [Member] Crude Oil [Member] Natural Gas [Member] Natural Gas [Member] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Midland Differential Basis Swaps [Member] Basis Swap [Member] Gulf Coast Differential Basis Swap [Member] Gulf Coast Differential Basis Swap [Member] Interest-rate swap contract where both rates are variable but are tied to different index rates. For example, but not limited to, one party's rate indexed to three-month London Interbank Offered Rate (LIBOR) while the other party's rate is indexed to six-month LIBOR. Price Swaps [Member] Swap [Member] Options [Member] Commodity Option [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Schedule of Derivative Instruments Schedule of Derivative Instruments [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Supplemental Cash Flow Information [Abstract] Net Cash Paid For Interest and Income Taxes Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Accounting Policies [Abstract] Statement [Table] Statement [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Amounts Without Adoption of ASU 2014-09 [Member] Accounting Standards Update 2014-09 [Member] Effect of Change [Member] Effect of Change [Member] Effect of change of adoption of ASU 2014-09 [Member] Statement [Line Items] Statement [Line Items] Crude Oil and Condensate Oil and Condensate Revenue Natural Gas Liquids Natural Gas Liquids Revenue from the sale of natural gas liquids. Natural Gas Natural Gas Production Revenue Gathering, Processing and Marketing Gas Gathering, Transportation, Marketing and Processing Revenue Total Revenues Gathering and Processing Costs Gas Gathering, Transportation, Marketing and Processing Costs Marketing Costs Marketing Costs Costs of purchasing third-party natural gas and crude oil and the related transportation costs. Total Costs and Expenses Operating Income (Loss) Operating Income (Loss) Accounts Receivable From Contracts With Customers Accounts Receivable, Net, Current Earnings Per Share [Abstract] Computation of Net Income Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Income Statement [Abstract] Operating Revenues and Other Revenues [Abstract] Gains (Losses) on Mark-to-Market Commodity Derivative Contracts Losses on Asset Dispositions, Net Other, Net Results of Operations, Revenue, Other Operating Expenses Cost of Revenue [Abstract] Lease and Well Oil and Gas Property, Lease Operating Expense Transportation Costs Results of Operations, Transportation Costs Gathering and Processing Costs Gathering and Processing Costs Operating and maintenance expenses and administrative expenses associated with operating gathering and processing assets. Exploration Costs Exploration Expense General and Administrative General and Administrative Expense Taxes Other Than Income Taxes Other Than Income Taxes other than income taxes, if not included elsewhere, could include, property tax or other selling and distribution-related taxes. Operating Income Other Income, Net Other Nonoperating Income (Expense) Income Before Interest Expense and Income Taxes Income Before Interest Expense and Income Taxes Income Before Interest Expense and Income Taxes. Interest Expense Interest Expense [Abstract] Interest Expense, Net Interest Expense Income Before Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income Tax Provision Income Tax Expense (Benefit) Net Income Net Income Per Share Earnings Per Share, Basic [Abstract] Basic Earnings Per Share, Basic Diluted Earnings Per Share, Diluted Dividends Declared per Common Share Common Stock, Dividends, Per Share, Declared Average Number of Common Shares Earnings Per Share, Basic, Other Disclosures [Abstract] Basic Weighted Average Number of Shares Outstanding, Basic Diluted Weighted Average Number of Shares Outstanding, Diluted Comprehensive Income Statement Of Comprehensive Income [Abstract] Comprehensive Income (Loss) Other Comprehensive Income Comprehensive Income (Loss) [Abstract] Foreign Currency Translation Adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Other, Net of Tax Other Comprehensive Income, Other, Net of Tax Other Comprehensive Income Other Comprehensive Income (Loss), Net of Tax Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Fair Value Disclosures [Abstract] Fair Value Assets and Liabilities Measured On Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Asset Retirement Obligation Rollforward Analysis Schedule of Asset Retirement Obligations [Table Text Block] Segment Reporting [Abstract] Selected Financial Information by Reportable Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Assets by Reportable Segment Reconciliation of Assets from Segment to Consolidated [Table Text Block] Share-based Arrangements with Employees and Nonemployees [Abstract] Share-based Arrangements with Employees and Nonemployees [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] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Lease And Well [Member] Lease And Well [Member] Name or caption of a line item on the balance sheet or income statement which was increased or decreased by share-based compensation costs during the period. Specifically, the Lease and Well category. Gathering And Processing Costs [Member] Gathering And Processing Costs [Member] Name or caption of a line item on the income statement which was increased or decreased by share-based compensation costs during the period. Specifically, the Gathering and Processing Costs category. Exploration Costs [Member] Exploration Costs [Member] Name or caption of a line item on the income statement which was increased or decreased by share-based compensation costs during the period. Specifically, the Exploration cost category. General And Administrative [Member] General And Administrative [Member] Name or caption of a line item on the income statement which was increased or decreased by share-based compensation costs during the period. Specifically, the General and Administrative category. Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Award Type and Plan Name [Axis] Award Type [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Equity Award [Domain] Stock Options and SARs [Member] Stock Options And Sars [Member] Stock options and stock-settled stock appreciations rights (SARS) ESPP [Member] Espp [Member] Employee Stock Purchase Plan Restricted Stock And Restricted Stock Units [Member] Restricted Stock And Restricted Stock Units [Member] Restricted Stock and Units which are not vested because the agreed upon employee services have not been received. Performance Units and Performance Stock [Member] Performance Shares [Member] Stock Options/SARs and Employee Stock Purchase Plan (ESPP) Disclosures [Line Items] Employee Stock Purchase Plan (ESPP) Disclosures [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Total Operating Expenses Compensation expense related to the company's stock-based compensation plans Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Stock-based compensation expense related to stock options, SAR and ESPP grants Allocated Share-based Compensation Expense Common Shares Available for Grant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period over which unrecognized compensation expense will be recognized (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Intrinsic value released during the year Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested Aggregate intrinsic value of stock and units outstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested Weighted Average Fair Values And Valuation Assumptions Used To Value Stock Option/SARs, ESPP, and Performance Units/Stock Stock-Based Compensation [Abstract] Weighted Average Fair Value And Valuation Assumptions Used To Value Stock Based Compensation [Abstract] Weighted Average Fair Value of Grants (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Expected Volatility (in hundredths) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-Free Interest Rate (in hundredths) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Dividend Yield (in hundredths) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected Life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Stock Options and SARs Rollforward [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at January 1 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Exercised (1) (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Outstanding at March 31 (2) (in shares) Stock Options and SARs Vested or Expected to Vest (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Stock Options and SARs Exercisable at September 30 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Intrinsic Value of Stock Options/SARs Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Intrinsic Value of Stock Options/SARs Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Weighted Average Remaining Contractual Life for Stock Options/SARs Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Intrinsic Value of Stock Options/SARs Vested or Expected to Vest Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Weighted average remaining contractual life for stock options/SARs vested or expected to vest (in years)al Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Aggregate Intrinsic Value for Exercisable Units Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Weighted average remaining contractual life for exercisable options/SARs (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted Average Grant Price Stock Option and SARs [Rollforward] Share Based Compensation Arrangement By Share Based Payment Award Options And Stock Appreciation Rights Additional Disclosures Abstract [Abstract] Outstanding at January 1 (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (price per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (1) (price per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forfeited (price per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Outstanding at March 31 (2) (price per share) Vested or Expected to Vest (3) (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Exercisable at March 31 (4) (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Restricted Stock/Restricted Stock Units [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-Based Compensation Arrangement By Restricted Stock And Restricted Stock Units Compensation Cost Restricted Stock or Unit Expense Outstanding at January 1 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Granted for Performance Multiple (1) Granted for Performance Multiple (1) Granted for Performance Multiple Released (1) (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at March 31 (2) (in shares) Weighted Average Grant Price Restricted Stock and Restricted Stock Units [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Outstanding at January 1 (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Granted for Performance Multiple (1) (in dollars per share) Granted for Performance Multiple (1) (in dollars per share) Granted for Performance Multiple Released (1) (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (price per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Outstanding at March 31 (2) (price per share) Performance Units and Performance Stock Disclosures [Abstract] Performance Units and Performance Stock [Abstract] Performance Units and Performance Stock Performance Period for Performance Units and Shares performance period for performance units and shares performance period for performance units and shares Minimum Performance Multiple at the Completion of the Performance Period Minimum Performance Multiple at the Completion of the Performance Period Minimum Performance Multiple to be Applied to Performance Stock/Units Granted at the Completion of the Performance Period Maximum Performance Multiple at the Completion of the Performance Period Maximum Performance Multiple at the Completion of the Performance Period Maximum Performance Multiple to be Applied to Performance Stock/Units Granted at the Completion of the Performance Period Minimum Performance Units and Stock Allowed to be Outstanding Minimum Performance Units and Stock Allowed to be Outstanding Minimum Performance Units and Stock Allowed to be Outstanding Maximum Performance Units and Stock Allowed to be Outstanding Maximum Performance Units and Stock Allowed to be Outstanding Maximum Performance Units and Stock Allowed to be Outstanding Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivatives, Fair Value, by Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Call Option [Member] Call Option [Member] Put Option [Member] Put Option [Member] Other Assets [Member] Other Assets [Member] Liabilities From Price Risk Management Activities [Member] Liabilities From Price Risk Management Activities [Member] Line item in the statement of financial position in which the fair value amounts of the derivative instruments are included. Other Liabilities [Member] Other Liabilities [Member] Assets From Price Risk Management Activities [Member] Assets From Price Risk Management Activities [Member] Line item in the statement of financial position in which the fair value amounts of the derivative instruments are included. Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Derivative Contracts - January through April (closed) [Member] Derivative Contracts January through April (closed) [Member] The derivative or group of derivatives on a disaggregated basis, such as for individual instruments, or small groups of similar instruments. Derivative Contracts - May through December [Member] Derivative Contracts May through December [Member] Derivative Contracts Year Two - January through December [Member] Derivative Contracts Year Two - January through December [Member] Derivative Contracts Year Two - January through December [Member] Derivative Contracts - January through March (closed) [Member] Derivative Contracts - January through March (closed) [Member] Derivative Contracts - January through March (closed) Derivative Contracts - April through December [Member] Derivative Contracts - April through December [Member] Derivative Contracts - April through December Derivative Contracts - March through April (closed) [Member] Derivative Contracts March through April (closed) [Member] Derivative Contracts March through April (closed) Derivative Contracts - May through November [Member] Derivative Contracts - May through November [Member] Derivative Contracts - May through November Price Risk Derivative [Member] Price Risk Derivative [Member] Volume (Bbld) Derivative, Nonmonetary Notional Amount, Volume Derivative, Swap Type, Average Fixed Price Derivative, Swap Type, Average Fixed Price Volume (MMBtud) Derivative, Nonmonetary Notional Amount, Energy Measure Derivative, Average Price Risk Option Strike Price Derivative, Average Price Risk Option Strike Price Assets from Price Risk Management Activities Derivative Asset, Current Other Assets Derivative Asset, Noncurrent Liabilities from Price Risk Management Activities Derivative Liability, Current Other Liabilities Derivative Liability, Noncurrent Derivative Collateral [Abstract] Derivative, Collateral [Abstract] Collateral Had on Derivative Derivative, Collateral, Right to Reclaim Cash Collateral Held on Derivative Derivative, Collateral, Obligation to Return Cash Exploratory Well Costs Suspended Well Costs Disclosure [Text Block] Net Income Per Share Earnings Per Share [Text Block] Discontinued Operations and Disposal Groups [Abstract] Proceeds from Sale of Oil and Gas Property and Equipment Schedule of Impact of Adoption of New Revenue Recognition Standard (Tables) Schedule of Prospective Adoption of New Accounting Pronouncements [Table Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Debt Disclosure [Abstract] Debt Instrument Table [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Debt Instrument Table [Line Items] Debt Instrument Table [Line Items] Debt Instrument [Abstract] Debt Instrument Issuance [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Eurodollar [Member] Eurodollar [Member] Base Rate [Member] Base Rate [Member] Line of Credit Facility [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Commercial Paper [Member] Commercial Paper [Member] Uncommitted Credit Facility [Member] Uncommitted Credit Facility [Member] Revolving Credit Agreement 2020 [Member] Senior Unsecured Revolving Credit Agreement New [Member] Senior Unsecured Revolving Credit Agreement New [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Borrowings Outstanding Line of Credit Facility, Current Borrowing Capacity Average Outstanding Amount Short-term Debt, Average Outstanding Amount Weighted average interest rate (in hundredths) Short-term Debt, Weighted Average Interest Rate, over Time Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Expiration Date Line of Credit Facility, Expiration Date Segment Information Segment Reporting Disclosure [Text Block] Risk Management Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward] Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward] Balance at January 1 Capitalized Exploratory Well Costs Additions Pending the Determination of Proved Reserves Capitalized Exploratory Well Cost, Additions Pending Determination of Proved Reserves Reclassifications to Proved Properties Reclassification to Well, Facilities, and Equipment Based on Determination of Proved Reserves Costs Charged to Expense Capitalized Exploratory Well Cost, Charged to Expense Balance at March 31 Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key 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 Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Retirement Benefits [Abstract] Schedule of Defined Benefit and Defined Contribution Plans Disclosures [Table] Schedule of Defined Benefit and Defined Contribution Plans Disclosures [Table] Defined Benefits and Defined Contribution Plans [Axis] Defined Benefits and Defined Contribution Plans [Axis] Defined Benefits and Defined Contribution Plans [Axis] Defined Benefits and Defined Contribution Plans [Domain] Defined Benefits and Defined Contribution Plans [Domain] [Domain] for Defined Benefits and Defined Contribution Plans [Axis] Defined Benefit and Defined Contribution Plan Disclosure [Line Items] Defined Benefit and Defined Contribution Plan Disclosure [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Total Pension Plans Costs Pension and Other Postretirement Benefits Cost (Reversal of Cost) Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Fair Value Measurements Fair Value, Measurement Inputs, Disclosure [Text Block] Fair Value Assets And Liabilities Measured On Recurring Basis [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Derivative Contract [Domain] Commodity Contract [Member] Commodity Contract [Member] Commodity Option [Member] Basis Swaps [Member] Options/Collars [Member] Commodity Options and Collars [Member] [Member] Commodity Options and Collars Fair Value Assets And Liabilities Measured On Recurring Basis Disclosure Items [Axis] Fair Value, Hierarchy [Axis] Fair Value Assets And Liabilities Measured On Recurring Basis [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Financial Assets: [Abstract] Assets, Fair Value Disclosure [Abstract] Assets, Fair Value Disclosure Assets, Fair Value Disclosure Financial Liabilities: Liabilities, Fair Value Disclosure [Abstract] Financial and Nonfinancial Liabilities, Fair Value Disclosure Financial and Nonfinancial Liabilities, Fair Value Disclosure Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets [Abstract] Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets [Abstract] Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets [Abstract] Proved Oil and Gas Properties and Other Assets Carrying Amount Proved Oil And Gas Properties, Other Property, Plant and Equipment and Other Assets, Carrying Amount Net dollar amount capitalized on balance sheet representing an enterprise's interests in proved crude oil (including condensate and natural gas liquids) and/or natural gas properties. Proved Oil and Gas Properties and Other Assets Written Down During the Period - Fair value at End of Period Proved Oil And Gas, Other Property, Plant and Equipment and Other Assets Property Fair Value Fair value of proved oil and gas property and other property, plant and equipment and other assets as of the balance sheet date. Pretax Impairment Charges for Proved Oil and Gas Properties and Other Assets Pretax Impairment Charges for Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets The expense recorded to reduce the value of oil and gas assets consisting of proved properties, other property, plant and equipment and other assets as the estimate of future successful production from these properties is reduced. Pretax Impairment Charge for a Commodity Price-Related Write-Down of Other Assets Pretax impairment charge for a commodity price-related write-down of other assets Pretax impairment charge for a commodity price-related write-down of other assets Debt Disclosure [Abstract] Aggregate Principal Amount of Current and Long-Term Debt Long-term Debt, Gross Estimated Fair Value of Debt Debt Instrument, Fair Value Disclosure Interest (1) Interest Paid, Net Income Taxes, Net of Refunds Received Income Taxes Paid, Net Interest Costs Capitalized Interest Costs Capitalized Accrued Capital Expenditures Capital Expenditures Incurred but Not yet Paid Non-Cash Property Exchanges Non-Cash Property Exchanges Increase in fair value related to non-cash property exchanges. Non-Cash Other Property, Plant and Equipment Non-Cash Other Property, Plant and Equipment Non-Cash Other Property, Plant and Equipment Related to Capital Lease Transaction Asset Retirement Obligations Asset Retirement Obligation Disclosure [Text Block] Selected Information [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment Information [Axis] Segments [Axis] Segment Information [Domain] Segments [Domain] United States [Member] UNITED STATES Trinidad [Member] TRINIDAD AND TOBAGO Other International [Member] Other International [Member] Selected Information [Line Items] Segment Reporting Information [Line Items] Schedule of Segment Reporting Information By Segment [Abstract] Segment Reporting Information, Revenue for Reportable Segment [Abstract] Operating Revenues and Other Total Assets Assets Pension and Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Long-Term Debt Long-term Debt [Text Block] Statement of Financial Position [Abstract] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] ASSETS Assets [Abstract] Current Assets Cash and Cash Equivalents, at Carrying Value [Abstract] Cash and Cash Equivalents Accounts Receivable, Net Receivables, Net, Current Inventories Inventory, Net Income Taxes Receivable Income Taxes Receivable, Current Other Other Assets, Current Total Assets, Current Property, Plant and Equipment Property, Plant and Equipment, Net [Abstract] Oil and Gas Properties (Successful Efforts Method) Oil and Gas Property, Successful Effort Method, Gross Other Property, Plant and Equipment Property, Plant and Equipment, Other, Gross Total Property, Plant and Equipment Property, Plant and Equipment, Gross Less: Accumulated Depreciation, Depletion and Amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Total Property, Plant and Equipment, Net Property, Plant and Equipment, Net Deferred Income Taxes Deferred Tax Assets, Net, Noncurrent Other Assets Other Assets, Noncurrent Total Assets Current Liabilities Liabilities, Current [Abstract] Accounts Payable Accounts Payable, Current Accrued Taxes Payable Taxes Payable, Current Dividends Payable Dividends Payable Current Portion of Long-Term Debt Long-term Debt, Current Maturities Other Other Liabilities, Current Total Liabilities, Current Long-Term Debt Long-term Debt, Excluding Current Maturities Other Liabilities Other Liabilities, Noncurrent Deferred Income Taxes Deferred Tax Liabilities, Net, Noncurrent Commitments and Contingencies (Note 8) Commitments and Contingencies Stockholders' Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common Stock, $0.01 Par, 1,280,000,000 Shares Authorized and 579,272,616 Shares Issued at March 31, 2018 and 578,827,768 Shares Issued at December 31, 2017 Common Stock, Value, Issued Additional Paid in Capital Additional Paid in Capital Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Retained Earnings Retained Earnings (Accumulated Deficit) Common Stock Held in Treasury, 459,990 Shares at March 31, 2018 and 350,961 Shares at December 31, 2017 Treasury Stock, Value Total Stockholders' Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total Liabilities and Stockholders' Equity Liabilities and Equity Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock Options And SARs [Member] Restricted Stock/Units and Performance Units/Stock [Member] Restricted Stock, Restricted Stock Units and Performance Units [Member] Restricted Stock, Restricted Stock Units and Performance Units [Member] Earnings Per Share, Diluted , By Common Class [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Numerator for Basic and Diluted Earnings Per Share - [Abstract] Earnings Per Share, Basic and Diluted [Abstract] Net Income Denominator for Basic Earnings Per Share - [Abstract] Weighted Average Shares Potential Dilutive Common Shares - [Abstract] Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangments Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Denominator for Diluted Earnings Per Share - [Abstract] Denominator For Diluted Earnings Per Share [Abstract] Adjusted Diluted Weighted Average Shares Antidilutive Securities Excluded from Computation of Earnings Per Share [Abstract] Antidilutive Securities Excluded from Computation of Earnings Per Share [Abstract] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Anti-dilutive Securities excluded from Diluted Earnings Per Share Calculation Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Net Income Per Share Net Income Loss Available To Common Stockholders [Abstract] Basic Diluted Supplemental Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] Common Stock Common Stock Common Stock Common Stock, Par Value (in dollars per share) Common Stock, Par or Stated Value Per Share Common Stock, Shares Authorized (in shares) Common Stock, Shares Authorized Common Stock, Shares Issued (in shares) Common Stock, Shares, Issued Treasury Stock (in shares) Treasury Stock Treasury Stock Common Stock Held in Treasury, Shares Treasury Stock, Shares Acquisitions and Divestitures Mergers, Acquisitions and Dispositions Disclosures [Text Block]