Debt Debt - Repayments (Details) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD	Dec. 31, 2015 USD ($)	Dec. 31, 2014 CAD
Extinguishment of Debt [Line Items]
Interest Expense, Debt	CAD 472	CAD 395		CAD 286
Secured Debt [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount		379	$ 285
Final repayment of principal amount		329	247
Debt Instrument, Early Redemption Premium		45	34
Interest Expense, Debt		5	$ 4
Debt Issuance Costs, Gross		CAD 2