Financial Instruments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 CAD	Jun. 30, 2015 CAD	Jun. 30, 2016 CAD	Jun. 30, 2015 CAD	Dec. 31, 2015 CAD	Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items]
Fair value	CAD 10,335,000,000		CAD 10,335,000,000		CAD 9,750,000,000
Gain (loss) on effective portion of derivative instrument designated as hedge		CAD 34,000,000	82,000,000	CAD 37,000,000
Derivative Instruments, Gain Recognized in Other Comprehensive Income (Loss), Effective Portion	32,000,000		84,000,000	39,000,000
Derivative losses amortized to net interest expense			(11,000,000)
Accounts Payable and Accrued Liabilities [Member]
Schedule of Investments [Line Items]
Derivative, Net Liability Position, Aggregate Fair Value	144,000,000		144,000,000		60,000,000
Net Interest Expense [Member]
Schedule of Investments [Line Items]
Derivative Instruments, Loss Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing	0	0	2,000,000	2,000,000
Amortized Net Interest Expensed [Member]
Schedule of Investments [Line Items]
Derivative Instruments, Gain Recognized in Other Comprehensive Income (Loss), Effective Portion	3,000,000	1,000,000	5,000,000	2,000,000
Forward Starting Interest Rate Swaps [Member]
Schedule of Investments [Line Items]
Floating-to-fixed interest rate swap agreements | $						$ 700
Net Investment Hedging [Member]
Schedule of Investments [Line Items]
Gain (loss) on effective portion of derivative instrument designated as hedge	24,000,000	CAD (58,000,000)	332,000,000	CAD (298,000,000)
Ineffectiveness			0
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Carrying value	CAD 8,581,000,000		CAD 8,581,000,000		CAD 8,957,000,000