Financial Instruments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 CAD	Mar. 31, 2016 CAD	Mar. 31, 2017 USD ($)	Dec. 31, 2016 CAD	Jun. 30, 2016 USD ($)
Schedule of Investments [Line Items]
Fair value of long-term debt	CAD 9,958,000,000			CAD 9,981,000,000
Gain (loss) on effective portion of derivative instrument designated as hedge	2,000,000	CAD (50,000,000)
Derivative, Gain (Loss)	2,000,000	(52,000,000)
Net Interest Expense [Member]
Schedule of Investments [Line Items]
Derivative ineffective portion loss	0	2,000,000
Amortized Net Interest Expensed [Member]
Schedule of Investments [Line Items]
Loss amortized to net interest expense	3,000,000	2,000,000
Derivative gain (loss) amortized to net interest expense	(11,000,000)
Accounts Payable and Accrued Liabilities [Member]
Schedule of Investments [Line Items]
Fair value loss	67,000,000			69,000,000
Forward Starting Interest Rate Swaps [Member]
Schedule of Investments [Line Items]
Floating-to-fixed interest rate swap agreements | $			$ 700		$ 700
Net Investment Hedging [Member]
Schedule of Investments [Line Items]
Gain (loss) on effective portion of derivative instrument designated as hedge	46,000,000	308,000,000
Amount of ineffectiveness on net investment hedges	0	CAD 0
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Carrying value of long-term debt	CAD 8,614,000,000			CAD 8,684,000,000