Income Taxes - Summary of Income Tax Expense (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Current income tax expense	CAD 73	CAD 159	CAD 177	CAD 364
Deferred income tax expense	50	0	233	106
Income tax expense	CAD 123	CAD 159	CAD 410	CAD 470