Income Taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD CAD in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2015	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Current income tax expense			CAD 373	CAD 208	CAD 38
Origination and reversal of temporary differences			105	317	183
Effect of tax rate increases			23	0	7
Effect of hedge of net investment in foreign subsidiaries			100	42	29
Other			6	(5)	(7)
Total deferred income tax expense			234	354	212
Income tax expense	CAD 23	CAD 7	607	562	250
Income before income tax expense
Canada			1,099	1,269	1,019
Foreign			860	769	106
Income before income tax expense			1,959	2,038	1,125
Current
Canada			173	50	4
Foreign			200	158	34
Total current income tax expense			373	208	38
Deferred
Canada			163	292	256
Foreign			71	62	(44)
Total deferred income tax expense			234	354	212
Income tax expense	CAD 23	CAD 7	CAD 607	CAD 562	CAD 250