Financial Instruments (Detail)	12 Months Ended
	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD	Dec. 31, 2014 CAD	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Short-term Investments	CAD 0	CAD 0
Fair Value of long-term debt	9,981,000,000	9,750,000,000
Long-term debt	8,684,000,000	8,957,000,000
Gain (loss) on effective portion of derivative instrument designated as hedge	(12,000,000)	(75,000,000)
Combined realized and unrealized foreign exchange gain (loss )	1,000,000	2,000,000
Unrealized gain (loss) derived from foreign exchange forward contract	1,000,000
Change in fair value loss	9,000,000	77,000,000
Accounts Payable and Accrued Liabilities [Member]
Schedule of Investments [Line Items]
Fair value loss	69,000,000	60,000,000
Accumulated Translation Adjustment [Member]
Schedule of Investments [Line Items]
Reclassification from AOCI	1,000,000	1,000,000
Forward Starting Interest Rate Swaps [Member]
Schedule of Investments [Line Items]
Floating-to-fixed interest rate swap agreements | $				$ 700,000,000	$ 700,000,000
Notional amount of interest rate swaps | $						$ 700,000,000	$ 700,000,000
Treasury Rate Locks [Member]
Schedule of Investments [Line Items]
Unamortized losses related to interest rate locks accounted as cash flow hedges	21,000,000	21,000,000
Net Investment Hedging [Member]
Schedule of Investments [Line Items]
Gain (loss) on effective portion of derivative instrument designated as hedge	150,000,000	(757,000,000)	CAD (319,000,000)
Amount of ineffectiveness on net investment hedges	0	0	CAD 0
Carrying Value Disclosure [Member]
Schedule of Investments [Line Items]
Debt and Capital Lease Obligations	8,684,000,000	8,957,000,000
2.900% 10-year Notes [Member] | Notes Payable to Banks [Member]
Schedule of Investments [Line Items]
Notional amount of interest rate swaps | $						700,000,000	700,000,000
Debt instrument face amount | $							$ 700,000,000
Interest rate							2.90%
6.125% 100-year Notes [Member] | Notes Payable to Banks [Member]
Schedule of Investments [Line Items]
Debt instrument face amount | $						$ 900,000,000
Interest rate						6.125%
Net Interest Expense [Member]
Schedule of Investments [Line Items]
Ineffective portion gain	3,000,000
Ineffective portion loss		2,000,000
Derivative losses amortized to net interest expense	11,000,000
Amortized Net Interest Expensed [Member]
Schedule of Investments [Line Items]
Loss amortized to net interest expense	CAD 11,000,000	CAD 6,000,000