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Employee Future Benefits - Status of Plans (Details) - CAD CAD in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | CAD (247) | CAD (230) |
Accrued current liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (12) | (22) |
Other long-term liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (235) | (208) |
Fair value of plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | 428 | 433 | CAD 438
Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (675) | (663) | (678)
Registered |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (145) | (131) |
Registered | Accrued current liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (4) | (15) |
Registered | Other long-term liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (141) | (116) |
Registered | Fair value of plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | 416 | 423 | 429
Registered | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (561) | (554) | (566)
Supplemental |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (75) | (72) |
Supplemental | Accrued current liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (6) | (6) |
Supplemental | Other long-term liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (69) | (66) |
Supplemental | Fair value of plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | 12 | 10 | 9
Supplemental | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (87) | (82) | (80)
Other |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (27) | (27) |
Other | Accrued current liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (2) | (1) |
Other | Other long-term liabilities |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | (25) | (26) |
Other | Fair value of plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | 0 | 0 | 0
Other | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net defined benefit liability (asset) | CAD (27) | CAD (27) | CAD (32)

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 140 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_140_a&doctype=Standard -URIDate 2017-03-09 + Details
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