Income Taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current income tax expense	$ 537	$ 525	$ 381
Origination and reversal of temporary differences	277	316	214
Effect of tax rate decrease	(32)	(95)	(21)
Effect of hedge of net investment in foreign subsidiaries	(18)	(38)	64
Other	(6)	(2)	(1)
Total deferred income tax expense (recovery)	221	181	256
Income tax expense	758	706	637
Income before income tax expense
Canada	2,518	2,392	1,788
Foreign	684	754	800
Income before income tax expense	3,202	3,146	2,588
Current
Canada	412	410	336
Foreign	125	115	45
Total current income tax expense	537	525	381
Deferred
Canada	231	141	174
Foreign	(10)	40	82
Total deferred income tax expense (recovery)	221	181	256
Income tax expense	$ 758	$ 706	$ 637