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Consolidated Statements of Comprehensive Income (Parenthetical) $ in Millions, $ in Billions | 12 Months Ended
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Dec. 31, 2017 CAD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 CAD ($) | Dec. 31, 2016 USD ($)
Consolidated Statements of Comprehensive Income [Abstract] |  |  |  |
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax | $ 0.0 |  | $ 3.0 |
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax |  | $ 1.2 |  | $ 1.2
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax | (9.0) |  | 0.0 |
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax | 1.0 |  | 0.0 |
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax | 1.0 |  | (3.0) |
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax | 0.0 |  | 9.0 |
Other Comprehensive Income Los sAvailable For Sale Securities Before Reclassification Adjustments Tax Other Equity Method | $ (7.0) |  | $ 9.0 |

X
- Definition Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities and unrealized holding gain (loss) related to transfers of securities into the available-for-sale category and out of the held-to-maturity category accounted for using other equity method. + References No definition available. + Details
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- Definition Amount of tax expense (benefit), before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 20 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=64808268&loc=d3e32211-110900 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e640-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580 + Details
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