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Income Taxes - Additional Information (Detail) - CAD
CAD in Millions
 12 Months Ended
Dec. 22, 2017
Dec. 31, 2017
Dec. 31, 2016
Major components of tax expense (income) [abstract]      
Effective income tax rate   26.75% 26.75%
Provisional charge for the estimated impact of U.S. Tax Reform, after-tax CAD 1,800    
Current tax receivable   CAD 778 CAD 446
Current tax payable   178 387
Deferred tax assets   4,569 4,439
Deferred tax assets - recognition dependent on future taxable profits   4,527 4,403
Operating tax loss carry forward   3,164 3,556
Operating tax loss carry forward expired in future   2,109  
Operating tax loss carry forward without expiration date   159  
Capital tax loss carry forward   8 9
Tax benefit on loss carry forwards for which deferred tax asset recognized   596 942
Tax benefit of loss carry forwards for which no deferred tax asset recognized   171 139
Tax credit carry forwards which expire in future   606 1,039
Tax credit carryforwards of which benefit not recognized   CAD 152 164
Tax credit/Loss carryforwards expiration period   Between the years 2020 and 2037  
Deferred tax liability   CAD 1,281 1,359
Aggregate amount of taxable temporary differences associated with the Company's own investments in subsidiaries, not included in financial statements   CAD 11,780 CAD 13,102