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Employee Benefit Plans (Amounts Recognized in the Consolidated Balance Sheets ) (Details) - CAD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract] |  |
Current Liabilities | $ (41) | $ (58)
Liabilities, Noncurrent | (559) | (669)
Pension Plan [Member] |  |
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract] |  |
Current Liabilities | (23) | (41)
Liabilities, Noncurrent | (264) | (367)
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent | 10 | 9
Deferred Tax Assets, Defined Benefit Plan | (15) | (16)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax | 548 | 620
Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total | 286 | 237
Non-pension Benefit Plans [Member |  |
Pension and Other Postretirement Defined Benefit Plans, Liabilities [Abstract] |  |
Current Liabilities | (18) | (17)
Liabilities, Noncurrent | (295) | (302)
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent | 0 | 0
Deferred Tax Assets, Defined Benefit Plan | (1) | 1
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax | 73 | 45
Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total | $ (239) | $ (275)

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to defined benfit plans. + References No definition available. + Details
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- Definition Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1731-114919 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(10)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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