Income Taxes - Summary of Income Tax Expense (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Current income tax expense	$ 140	$ 142	$ 286	$ 243
Deferred income tax expense (recovery)	49	(18)	88	20
Income tax expense	$ 189	$ 124	$ 374	$ 263