Income Taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 525	$ 381	$ 303
Origination and reversal of temporary differences	316	214	371
Effect of tax rate decrease	(95)	(21)	(541)
Effect of hedge of net investment in foreign subsidiaries	(38)	64	(42)
Other	(2)	(1)	2
Total deferred income tax expense (recovery)	181	256	(210)
Income tax expense	706	637	93
Income before income tax expense
Canada	2,392	1,788	1,829
Foreign	754	800	669
Income before income tax expense	3,146	2,588	2,498
Current
Canada	410	336	257
Foreign	115	45	46
Total current income tax expense	525	381	303
Deferred
Canada	141	174	256
Foreign	40	82	(466)
Total deferred income tax expense (recovery)	181	256	(210)
Income tax expense	$ 706	$ 637	$ 93