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Employee Future Benefits - Fair Value of Plan Assets (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | $ (238) |  |
Administration expenses | (2) | $ (1) | $ (2)
Net asset, ending of period | (278) | (238) |
Plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | 381 | 428 |
Interest on plan assets | 13 | 13 | 15
Net return on plan assets | 40 | (25) |
Contributions | 11 | 12 |
Benefits paid | (56) | (48) |
Effect of translation on US plans | (1) | 2 |
Net asset, ending of period | 386 | 381 | 428
Registered |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | (146) |  |
Administration expenses | (2) | (1) | (2)
Net asset, ending of period | (170) | (146) |
Registered | Plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | 368 | 416 |
Interest on plan assets | 12 | 13 | 15
Net return on plan assets | 40 | (25) |
Contributions | 6 | 5 |
Benefits paid | (50) | (42) |
Effect of translation on US plans | (1) | 2 |
Net asset, ending of period | 373 | 368 | 416
Supplemental Pension Plan |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | (67) |  |
Administration expenses | 0 | 0 | 0
Net asset, ending of period | (86) | (67) |
Supplemental Pension Plan | Plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | 13 | 12 |
Interest on plan assets | 1 | 0 | 0
Net return on plan assets | 0 | 0 |
Contributions | 4 | 6 |
Benefits paid | (5) | (5) |
Effect of translation on US plans | 0 | 0 |
Net asset, ending of period | 13 | 13 | 12
Other |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | (25) |  |
Administration expenses | 0 | 0 | 0
Net asset, ending of period | (22) | (25) |
Other | Plan assets |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Net asset, beginning of period | 0 | 0 |
Interest on plan assets | 0 | 0 | 0
Net return on plan assets | 0 | 0 |
Contributions | 1 | 1 |
Benefits paid | (1) | (1) |
Effect of translation on US plans | 0 | 0 |
Net asset, ending of period | $ 0 | $ 0 | $ 0

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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 141 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_f&doctype=Standard -URIDate 2018-03-16 + Details
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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 increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 141 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_e&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 141 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_b&doctype=Standard -URIDate 2018-03-16 + 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 2018-01-01 -Paragraph 140 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_140_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan in respect of settlements. [Refer: Gains (losses) arising from settlements, net defined benefit liability (asset); Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 141 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_g&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets, excluding amounts included in interest income or expense. The return on plans assets is interest, dividends and other revenue derived from the plan assets, together with realised and unrealised gains or losses on the plan assets, less any costs of managing plan assets and less any tax payable by the plan itself, other than tax included in the actuarial assumptions used to measure the present value of the defined benefit obligation. [Refer: Plan assets [member]; Net defined benefit liability (asset); Actuarial assumptions [member]; Interest expense (income), net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 141 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_c_i&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition Administrative Expenses, Net Defined Benefit Liability (Asset) + References No definition available. + Details
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- Details
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