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Accumulated Other Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | $ 106 | $ 137
Other comprehensive income (loss) before reclassifications | (345) | 0
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | 51 | 19
Other equity method reclassification adjustment | 0 | (46)
Net current period other comprehensive income (loss) | (294) | (27)
Other | 0 | (4)
Ending Balance | (188) | 106
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | (21) | (35)
Other comprehensive income (loss) before reclassifications | 10 | 11
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | 8 | 11
Other equity method reclassification adjustment | 0 | (8)
Net current period other comprehensive income (loss) | 18 | 14
Other | 0 | 0
Ending Balance | (3) | (21)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | (309) | (318)
Other comprehensive income (loss) before reclassifications | 0 | 0
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | 44 | 12
Other equity method reclassification adjustment | 0 | (3)
Net current period other comprehensive income (loss) | 44 | 9
Other | 0 | 0
Ending Balance | (265) | (309)
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | (49) | 0
Other comprehensive income (loss) before reclassifications | 97 | (49)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | 0 | 0
Other equity method reclassification adjustment | 0 | 0
Net current period other comprehensive income (loss) | 97 | (49)
Other | 0 | 0
Ending Balance | 48 | (49)
Accumulated Net Available For Sale Securities Gain (Loss) [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | (1) | 0
Other comprehensive income (loss) before reclassifications | 5 | 3
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | (1) | (4)
Other equity method reclassification adjustment | 0 | 0
Net current period other comprehensive income (loss) | 4 | (1)
Other | 0 | 0
Ending Balance | 3 | (1)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Beginning Balance | 486 | 490
Other comprehensive income (loss) before reclassifications | (457) | 35
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent | 0 | 0
Other equity method reclassification adjustment | 0 | (35)
Net current period other comprehensive income (loss) | (457) | 0
Other | 0 | (4)
Ending Balance | $ 29 | $ 486

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- Definition Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, attributable to parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners). + References No definition available. + Details
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