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Financial Instruments - Additional Information (Detail) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Customer	Dec. 31, 2015 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD
Derivative Instruments, Gain (Loss) [Line Items]
Trading securities	$ 1,034	$ 2,940
Long-term debt due within one year	$ 139	$ 211
Debt instrument maturity period	1 year
Book value of senior notes	$ 2,300
Sales Revenue, Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of largest customers | Customer	6
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Percentage of sales to six largest customers	82.00%	83.00%
Fair Value, Inputs, Level 1 [Member] | Senior Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Estimated fair value of notes payable	$ 2,360
Asset-backed Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Face value of investments | CAD			CAD 81	CAD 107
Asset-backed Securities [Member] | Reported Value Measurement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Trading securities | CAD			81	CAD 101
Asset-backed Securities [Member] | Estimate of Fair Value Measurement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Trading securities | CAD			CAD 81
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange forward contracts, gain recognized in other comprehensive loss	18
Foreign exchange forward contracts, loss recognized in other comprehensive loss	$ 195

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Maturity period of term loan facility under sub tranche.

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Number of largest customers.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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The effective portion of gains on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair value portion of notes payable.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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Cost of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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