Amortization of postretirement benefits liability adjustment included in net benefit cost Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income Accumulated Defined Benefit Plans Adjustment Before Tax [Member] Changes to accumulated comprehensive income related to benefit plans, before tax. Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Pay vs Performance Disclosure [Line Items] Total current assets Assets, Current Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Finance lease obligations - reduction (note 6) Finance Lease, Principal Payments Net benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) All Individuals All Individuals [Member] All Award Types Award Type [Domain] Fair Value as of Grant Date Award Grant Date Fair Value Effect of counterparty netting Derivative Fair Value Of Derivative Amount Effect Of Counter party netting [Member] Derivative Fair Value Of Derivative Amount Effect Of Counter party netting [Member] Entity Filer Category Entity Filer Category Statement of Stockholders' Equity [Abstract] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Statement [Table] Statement [Table] Effect of collateral netting Derivative Fair Value Of Derivative Amount Effect Of Collateral Netting [Member] Derivative Fair Value Of Derivative Amount Effect Of Collateral Netting [Member] Current Fiscal Year End Date Current Fiscal Year End Date Postretirement benefits liability adjustment (excluding amortization) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax Included contributions to registered pension plans Contribution To Registered Pension Plan Assets The amount of cash contributed to the registered pension plan assets. Amortization of postretirement benefits liability adjustment included in net benefit costs Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Segment Reporting [Abstract] PEO Name PEO Name Restatement Determination Date: Restatement Determination Date [Axis] Proceeds from asset sales Proceeds from Sales of Assets, Investing Activities Undiscounted commitments Lessee Operating Lease Lease Not yet Commenced Undiscounted Commitments Lessor, Operating Lease, Lease Not yet Commenced, Undiscounted Commitments Changes in accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Insider Trading Policies and Procedures [Line Items] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Other postretirement benefits: Other Postretirement Benefits Plan [Member] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Cash flows from (used in) operating activities Cash flows from (used in) operating activities Net Cash Provided by (Used in) Operating Activities Deferred income tax liabilities Deferred Tax and Other Liabilities, Noncurrent Geographical [Axis] Geographical [Axis] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Corporate and other Corporate, Non-Segment [Member] All other items - net Increase (Decrease) in Other Operating Assets and Liabilities, Net Depreciation and depletion Depreciation, Depletion and Amortization Capital and exploration expenditures Capital And Exploration Expenditures Sum of exploration expenses, additions to property, plant, equipment and intangible and additions to capital leases. Accounts payable and accrued liabilities (note 7) Accounts Payable and Accrued Liabilities, Current Current liabilities Liabilities, Current [Abstract] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Statement of Financial Position [Abstract] Total shareholders’ equity At beginning of period At end of period Equity, Attributable to Parent Intersegment Eliminations Intersegment Eliminations [Member] Consolidation Items [Axis] Consolidation Items [Axis] Dividends paid Payments of Ordinary Dividends, Common Stock Chemical Chemical [Member] Chemical [Member] Net income (loss) per common share - diluted (note 9) (in CAD per share) Net income (loss) per common share (dollars) Earnings Per Share, Diluted PEO Total Compensation Amount PEO Total Compensation Amount Investment and other income (note 3) Investment and other income (note 3) Investment And Other Income Net Investment and other income net. Purchases of crude oil and products Amounts to related parties included in purchases of crude oil and products Purchases of crude oil and products Crude Oil And Product Purchases Purchase cost of crude oil, products and other raw materials, feedstocks, semi finished products, finished products and other merchandise that become part of salable products for oil and gas, refining and marketing and chemical operations. Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Accounts receivable, net, related party amount Receivables, Net Of Accounts Payable And Accrued Liabilities, Current Receivables, Net Of Accounts Payable And Accrued Liabilities, Current Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Level 3 Fair Value, Inputs, Level 3 [Member] Debt-related interest Interest and Debt Expense Long-term debt (note 6) Total long-term debt Long-Term Debt and Lease Obligation Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Schedule of net benefit costs Schedule of Net Benefit Costs [Table Text Block] Downstream Downstream [Member] Downstream [Member] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Employee retirement benefit obligations in current liabilities Liability, Defined Benefit Plan, Current Level 2 Fair Value, Inputs, Level 2 [Member] Long-term debt, fair value Long-Term Debt, Fair Value Net income (loss) Net income (loss) Net income (loss) for the period Net Income (Loss) Total current liabilities Liabilities, Current Derivative Contract [Domain] Derivative Contract [Domain] Schedule of Notional Amounts of Outstanding Derivative Positions Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Company Selected Measure Name Company Selected Measure Name Asset retirement obligations and other environmental liabilities in current liabilities Asset Retirement Obligation And Other Environmental Liabilities Current Asset retirement obligation and other environmental liabilities current. Additions to property, plant and equipment Payments to Acquire Productive Assets Derivative Instruments, Gain (Loss) Derivative Instruments, Gain (Loss) [Table Text Block] Income tax expense (credit) for components of other comprehensive income (loss) Schedule Of Income Tax Expense For Components Of Comprehensive Income [Table Text Block] Schedule Of Income Tax Expense For Components Of Comprehensive Income Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Shareholders’ equity Equity, Attributable to Parent [Abstract] Amounts reclassified from accumulated other comprehensive income Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Derivative, Nonmonetary Notional Amount, Volume Derivative, Nonmonetary Notional Amount, Volume Loans to equity companies - net Net Movement Related To Loans To Equity Companies Net movement related to loans to equity companies. Document Fiscal Period Focus Document Fiscal Period Focus Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Calculation of basic and diluted earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Service cost Defined Benefit Plan, Service Cost Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Title Trading Arrangement, Individual Title Production and manufacturing Production and manufacturing Production And Manufacturing Expenses Costs, excluding deprecation, incurred to operate and maintain - 1) oil and gas wells, production, transportation and support equipment and facilities; 2) refining manufacturing facilities; and 3) chemical manufacturing facilities. Executive Category: Executive Category [Axis] Position [Domain] Position [Domain] Operating revenues Operating Revenues Including Federal Excise Tax Total revenue from sales of goods and services during the reporting period, reduced by sales returns and allowances and sales discounts. Also includes federal excise tax which is then deducted as an expense. Common shares at stated value (note 9) Common Stock Common Stock [Member] Federal excise tax and fuel charge Federal Excise Tax And Fuel Charge The amount of federal excise tax and fuel charge included in sales and revenues, which are then deducted as an expense. Level 1 Fair Value, Inputs, Level 1 [Member] Name Measure Name Individual: Individual [Axis] Name Forgone Recovery, Individual Name City Area Code City Area Code Entity Address, Postal Zip Code Entity Address, Postal Zip Code Net carrying value Reported Value Measurement [Member] Goodwill Goodwill Equity Components [Axis] Equity Components [Axis] Financial Instruments And Derivatives [Table] Financial Instruments And Derivatives [Table] Financial Instruments And Derivatives [Table] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Document Fiscal Year Focus Document Fiscal Year Focus Geographical [Domain] Geographical [Domain] Underlying Securities Award Underlying Securities Amount Entity Small Business Entity Small Business Other comprehensive income (loss) information Comprehensive Income (Loss) Note [Text Block] Local Phone Number Local Phone Number Accounts receivable Increase (Decrease) in Accounts Receivable Property, plant and equipment, net Property, Plant and Equipment, Net Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Accounts receivable - net Receivables, Net, Current Exercise Price Award Exercise Price Dividends per common share – declared (dollars) Common Stock, Dividends, Per Share, Declared Materials, supplies and prepaid expenses Materials Supplies And Prepaid Expenses Carrying amount as of the balance sheet date for elements of machinery or equipment held for the purpose of replacing similar parts in the course of repair or maintenance. Expenditures made in advance of when the economic benefit of the cost will be realized, and which will be expensed in future periods with the passage of time or when a triggering event occurs. Capitalized interest Interest Paid, Capitalized, Investing Activities Book value of asset sales Book Value Of Assets Sold Book Value of Assets Sold Statement of Cash Flows [Abstract] Depreciation and depletion Depreciation Depletion and Amortization Excluding Intangible Asset Impairment Charges The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets or depleting assets to periods that benefit from use of the assets but excludes impairment of specifically identified intangible assets associated with carbon emission cap and trade intangible assets. Assets Assets [Abstract] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Operating lease liability Operating Lease, Liability, Noncurrent Retirement Plan Type [Domain] Retirement Plan Type [Domain] Summary of estimated fair value of financial instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Liabilities Derivative Liability [Abstract] Liabilities Liabilities [Abstract] Retirement Benefits [Abstract] Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Amortization of postretirement benefits liability adjustment included in net benefit cost Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Income taxes (paid) refunded. Income Taxes Paid, Net Cash flows from (used in) financing activities Net Cash Provided by (Used in) Financing Activities Other obligations Other Sundry Liabilities, Noncurrent Retirement Plan Type [Axis] Retirement Plan Type [Axis] Long-term debt Schedule of Long-Term Debt Instruments [Table Text Block] Earnings reinvested Retained Earnings [Member] Employee retirement benefits Liability, Defined Benefit Plan, Noncurrent Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Total liabilities and shareholders’ equity Liabilities and Equity Other assets, including intangibles - net Other Assets, Noncurrent Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Effect of employee share-based awards (millions of shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Net income (loss) per common share - basic (note 9) (in CAD per share) Net income (loss) per common share (dollars) Earnings Per Share, Basic Accounting Policies [Abstract] Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] (Gain) loss on asset sales (note 3) Gain (loss) on asset sales, before tax Gain (Loss) on Disposition of Assets Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Income taxes payable Accrued Income Taxes, Current Total revenues and other income Revenues Arrangement Duration Trading Arrangement Duration Other Performance Measure, Amount Other Performance Measure, Amount Net interest expense Interest Expense, Debt Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Derivative collateral receivable Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Not Offset Entity Address, City or Town Entity Address, City or Town Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Business segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Related Party Related Party [Member] Investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Award Type Award Type [Axis] Derivative Instruments and Hedging Activities Disclosure [Abstract] Document Quarterly Report Document Quarterly Report Asset retirement obligations and other environmental liabilities Asset Retirement Obligation And Other Environmental Liabilities Noncurrent Asset retirement obligation and other environmental liabilities, noncurrent. Financing Amounts to related parties included in financing Financing (note 5) Total financing Interest Expense Deferred income taxes and other Deferred Income Taxes and Other The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations. Prior year Exploration and Exploratory dry hole costs written off as expense in the current year. Entity's net proportionate share for the period of net earnings, less dividends, of its investment to which the equity method of accounting is applied. Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Document Transition Report Document Transition Report Award Timing Predetermined Award Timing Predetermined [Flag] Property, plant and equipment, Property, Plant and Equipment, Gross Trading Arrangement: Trading Arrangement [Axis] Termination Date Trading Arrangement Termination Date Crude Oil Crude Oil [Member] Summary of common shares Summary Of Common Shares [Table Text Block] Summary of common shares authorized. Common shares authorized (in shares) Authorized (in shares) Common Stock, Shares Authorized PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Schedule of Investments [Abstract] Entity File Number Entity File Number Lease liability due within one year, Operating leases Operating Lease, Liability, Current Revenues Amounts from related parties included in revenues Total Revenues Including Federal Excise Tax Total revenue from sales of goods and services during the reporting period, reduced by sales returns and allowances and sales discounts. Also includes federal excise tax which is then deducted as an expense. Schedule of Other Liabilities [Table] Other Liabilities Disclosure [Abstract] Entity Address, Country Entity Address, Country Derivative Instrument [Axis] Derivative Instrument [Axis] Entity Shell Company Entity Shell Company Current period change excluding amounts reclassified from accumulated other comprehensive income OCI, before Reclassifications, Net of Tax, Attributable to Parent Adjustments for non-cash items: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] All Trading Arrangements All Trading Arrangements [Member] Restatement Determination Date Restatement Determination Date Revenue outside the scope of ASC 606 Revenue Not from Contract with Customer All Adjustments to Compensation All Adjustments to Compensation [Member] Derivative [Line Items] Derivative [Line Items] Upstream Upstream [Member] Upstream [Member] Income taxes payable Increase (Decrease) in Income Taxes Payable Award Timing Disclosures [Line Items] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Compensation Amount Outstanding Recovery Compensation Amount Financing costs and additional notes and loans payable information [Abstract] Financing costs and additional notes and loans payable information Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Products Products Barrels [Member] Products barrels. Other comprehensive income (loss), net of income taxes Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Derivative Asset Derivative Asset Financing costs Schedule Of Financing Cost [Table Text Block] Schedule of financing cost Eliminations Consolidation, Eliminations [Member] Statement of Comprehensive Income [Abstract] Accumulated other comprehensive income (loss) (note 10) Balance at January 1 Balance at March 31 Accumulated Other Comprehensive Income (Loss), Net of Tax Employee Stock Option Employee Stock Option [Member] Financial and derivative instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Notes and loans payable Debt, Current Total expenses Costs and Expenses Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Insider Trading Arrangements [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Document Type Document Type Inventories of crude oil and products Inventory, Finished Goods and Work in Process, Gross Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Related Party, Type [Axis] Related Party, Type [Axis] Tabular List, Table Tabular List [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Common shares outstanding (in shares) Common stock beginning balance, (in shares) Common stock, ending balance, (in shares) Common Stock, Other Shares, Outstanding Investment and other income Interest and Other Income [Table Text Block] Entity Address, Address Line One Entity Address, Address Line One Entity Registrant Name Entity Registrant Name Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Award Timing Method Award Timing Method [Text Block] Energy [Domain] Energy [Domain] Adjustment to Compensation, Amount Adjustment to Compensation Amount Proceeds from asset sales (note 3) Proceeds from Sale of Property, Plant, and Equipment Revenues Realized And Unrealized Revenue On Derivative Instrument Total realized and unrealized revenue on derivative instrument. Document Period End Date Document Period End Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Adoption Date Trading Arrangement Adoption Date Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] less accumulated depreciation and depletion Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Gain (loss) on asset sales, after tax Net Gain (Loss) On Asset Sales After Tax Net gain (loss) on asset sales, after tax. Finance leases Finance Lease, Liability, Noncurrent Entity Central Index Key Entity Central Index Key Selling and general Selling and General Selling And General Exploration Exploration Exploration Expense Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Derivative [Table] Derivative [Table] Basis of financial statement preparation Basis of Presentation and Significant Accounting Policies [Text Block] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Net income (loss) per common share – diluted Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Income taxes Income Tax Expense (Benefit) Income Statement [Abstract] Amounts to related parties included in production and manufacturing, and selling and general expenses Production And Manufacturing Expense And Selling and General Expense Production And Manufacturing Expense And Selling and General Expense Revenue from contracts with customers Revenue from Contract with Customer, Including Assessed Tax Expenses Costs and Expenses [Abstract] Energy [Axis] Energy [Axis] Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Share-based incentive compensation liabilities Deferred Compensation Share-Based Arrangements, Liability, Classified, Noncurrent Name Trading Arrangement, Individual Name Total other comprehensive income (loss) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Related Party, Type [Domain] Related Party, Type [Domain] Derivative liabilities Derivative Liability Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Operating Segments Operating Segments [Member] Equity [Abstract] Entity [Domain] Entity [Domain] Class of Stock [Line Items] Class of Stock [Line Items] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Amendment Flag Amendment Flag Inventories, materials, supplies and prepaid expenses Increase (Decrease) in Inventories Materials and Supplies and Prepaid Expenses The net change during the reporting period in the aggregate value of all inventory, materials and supplies held by the reporting entity, associated with underlying transactions that are classified as operating activities. And the net change during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods. Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Legal Entity [Axis] Legal Entity [Axis] Amortization of actuarial loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Entity Tax Identification Number Entity Tax Identification Number Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Interest (paid), net of capitalization. Interest Paid, Excluding Capitalized Interest, Operating Activities Purchases at stated value, (in shares) Stock Repurchased and Retired During Period, Shares Entity Interactive Data Current Entity Interactive Data Current Long-term debt Long-Term Debt [Text Block] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Net income (loss) per common share – basic Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Long-term debt, related party amount Long-term debt Long-Term Debt, Excluding Current Maturities Total Shareholder Return Amount Total Shareholder Return Amount Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Common shares purchased (note 9) Payments for Repurchase of Common Stock Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Weighted-average number of common shares outstanding, assuming dilution (millions of shares) Weighted Average Number of Shares Outstanding, Diluted Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Total Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Other interest Interest Income Expense Other Amount of the cost of borrowed funds accounted for as interest expense. Segments [Domain] Segments [Domain] Common shares Common Share Information And Schedule Of Earnings Per Share Calculations [Text Block] Common share information and schedule of earnings per share calculations Assets Derivative Asset [Abstract] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Other long-term obligations Other Noncurrent Liabilities [Table Text Block] Consolidation Items [Domain] Consolidation Items [Domain] Earnings reinvested Retained Earnings (Accumulated Deficit) Measure: Measure [Axis] Name Outstanding Recovery, Individual Name Company Selected Measure Amount Company Selected Measure Amount Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Current assets Assets, Current [Abstract] Non-service pension and postretirement benefit Non-service pension and postretirement benefit Pension And Post Retirement Benefit Costs Non Service Components Pension and post retirement benefit costs non service components. Total assets Total assets as at March 31 Assets Name Awards Close in Time to MNPI Disclosures, Individual Name Entity Address, State or Province Entity Address, State or Province Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Short Short [Member] Cover [Abstract] Position [Axis] Position [Axis] Operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] United States Exports UNITED STATES Common shares outstanding (in shares) Common Stock, Shares, Outstanding Financial Instruments And Derivatives [Line Items] Financial Instruments And Derivatives [Line Items] Financial Instruments And Derivatives [Line Items] Other long-term obligations Other Liabilities Disclosure [Text Block] Investment and other income Interest and Other Income [Text Block] Dividends declared Dividends Other long-term obligations (note 7) Total other long-term obligations Other Liabilities, Noncurrent Interest cost Defined Benefit Plan, Interest Cost Non-NEOs Non-NEOs [Member] Other Income and Expenses [Abstract] PEO PEO [Member] Share purchases in excess of stated value Share Purchases In Excess Of Stated Value Excess of the purchase price of common stock over the stated value charged to retain earnings during the period Employee retirement benefits Retirement Benefits [Text Block] Common share activities Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Pension benefits: Pension Plan [Member] Business segments Segment Reporting Disclosure [Text Block] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Increase (decrease) in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Non-PEO NEO Non-PEO NEO [Member] Equity Component [Domain] Equity Component [Domain] Adjustment to Compensation: Adjustment to Compensation [Axis] Cash flows from (used in) investing activities Net Cash Provided by (Used in) Investing Activities Amounts reclassified out of accumulated other comprehensive income (loss) - before tax income (expense) Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Weighted-average number of common shares outstanding (millions of shares) Weighted Average Number of Shares Outstanding, Basic Postretirement benefits liability adjustment (excluding amortization) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax Share purchases at stated value Purchases at stated value Stock Repurchased and Retired During Period, Value Entity Current Reporting Status Entity Current Reporting Status Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Total liabilities Liabilities Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Investments and long-term receivables Investments and long-term receivables, related party amount Long-Term Investments and Receivables, Net Revenues and other income Revenues [Abstract] Accumulated other comprehensive income (loss) (note 10) AOCI Attributable to Parent [Member] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount All Executive Categories All Executive Categories [Member] Financing costs Financing costs and additional notes and loans payable information [Text Block] The disclosure for the amount of the cost of financing and information relating to notes and loans payable. Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Master netting arrangements Master netting arrangements [Member] Master netting arrangements [Member] Segments [Axis] Segments [Axis] Statement of Partners' Capital [Abstract] Statement [Line Items] Statement [Line Items] Accumulated Defined Benefit Plans Adjustment Attributable to Parent Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Debt Disclosure [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Per share information (Canadian dollars) Earnings Per Share [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Common shares at stated value (note 9) Common stock beginning balance Common stock, ending balance Common Stock, Value, Issued