Income Taxes - Narrative (Details) - CAD CAD in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Foreign exchange gain on U.S. dollar-denominated debt	CAD 181
Estimated annual effective tax rate	27.50%	27.50%
Effective tax rate	23.90%	29.50%