Income Taxes - Summary of Income Tax Expense (Details) - CAD CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Current income tax expense	CAD 27	CAD 103	CAD 104	CAD 205
Deferred income tax expense	90	74	183	106
Income tax expense	CAD 117	CAD 177	CAD 287	CAD 311