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Financial Instruments - Additional Information (Detail) CAD in Millions, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2015 USD ($) Customer | Dec. 31, 2015 CAD | Dec. 31, 2014 USD ($) | Dec. 31, 2014 CAD
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Trading Securities | $ 2,940 |  | $ 1,337 |
Long-term debt due within one year | $ 211 |  | $ 183 |
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 | 83.00% |  |  |
Asset-backed Securities [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Face value of investments | CAD |  | CAD 107 |  | CAD 107
Trading Securities | CAD |  | CAD 101 |  | CAD 102
Fair Value, Inputs, Level 1 [Member] | Senior Notes [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Estimated fair value of notes payable | $ 2,310 |  |  |
Forward Contracts [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Foreign exchange forward contracts, gain recognized in other comprehensive loss | 31 |  |  |
Foreign exchange forward contracts, loss recognized in other comprehensive loss | $ (343) |  |  |

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