Income Taxes - Summary of Income Tax Expense (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Current income tax expense	$ 248	$ 140	$ 388	$ 286
Deferred income tax expense	9	49	60	88
Income tax expense	$ 257	$ 189	$ 448	$ 374