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Income Taxes - Significant Components of Deferred Income Tax Assets (Liabilities) (Details) - CAD ($)
$ in Millions
Dec. 31, 2022
Dec. 31, 2021
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Unrecognized deferred income tax assets $ (50) $ (64)
Net deferred income tax liability, after write-down of deferred income tax assets (302) (290)
Cost | Non-capital losses    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 244 530
Cost | Future decommissioning and restoration costs    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 119 183
Cost | Property, plant and equipment    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets (553) (651)
Cost | Risk management assets and liabilities, net    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 193 (53)
Cost | Employee future benefits and compensation plans    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 48 53
Cost | Interest deductible in future periods    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 0 17
Cost | Foreign exchange differences on US-denominated debt    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 13 16
Cost | Other deductible temporary differences    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets (5) (5)
Accumulated impairment    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Net deferred income tax asset, before write-down of deferred income tax assets 59 90
Unrecognized deferred income tax assets $ (361) $ (380)