Financial Instruments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 CAD	Sep. 30, 2015 CAD	Sep. 30, 2016 CAD	Sep. 30, 2015 CAD	Jun. 30, 2016 USD ($)	Dec. 31, 2015 CAD	Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items]
Fair value	CAD 10,553,000,000		CAD 10,553,000,000			CAD 9,750,000,000
Gain (loss) on effective portion of derivative instrument designated as hedge	0	CAD (45,000,000)	(82,000,000)	CAD (82,000,000)
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Gain), Effective Portion	0	46,000,000	84,000,000	85,000,000
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	1,000,000	2,000,000	3,000,000
Amortized Net Interest Expensed [Member]
Schedule of Investments [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	3,000,000	1,000,000	8,000,000	4,000,000
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	(72,000,000)	CAD (291,000,000)	260,000,000	CAD (589,000,000)
Ineffectiveness			0
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Carrying value	CAD 8,879,000,000		CAD 8,879,000,000			CAD 8,957,000,000