Income Taxes - Summary of Income Tax Expense (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Current income tax expense	$ 142	$ 85	$ 243	$ 166
Deferred income tax (recovery) expense	(18)	37	20	78
Income tax expense	$ 124	$ 122	$ 263	$ 244