Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets and liabilities [abstract]
Deferred tax assets	CAD 4,569	CAD 4,439
Deferred tax liabilities	(1,281)	(1,359)
Net deferred tax assets	CAD 3,288	CAD 3,080	CAD 2,832

The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]]

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