Pension Plans and Other Post-Retirement Benefits - Schedule of Components of Defined Benefit Costs Recognized In Other Comprehensive Income (Loss) (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Disclosure of defined benefit plans [line items]
Return on plan assets (excluding amounts included in net interest expense)	$ (234)	$ 305
Actuarial gains (losses) arising from changes in demographic assumptions	2	(1)
Actuarial gains (losses) arising from changes in financial assumptions	200	(297)
Actuarial gains (losses) arising from experience adjustments	(13)	21
Foreign exchange rate movement	(3)	2
Components of defined benefit costs recognized in Other comprehensive income (loss)	(48)	30
Pension
Disclosure of defined benefit plans [line items]
Return on plan assets (excluding amounts included in net interest expense)	(234)	305
Actuarial gains (losses) arising from changes in demographic assumptions	2	(3)
Actuarial gains (losses) arising from changes in financial assumptions	187	(278)
Actuarial gains (losses) arising from experience adjustments	(20)	3
Foreign exchange rate movement	(3)	0
Components of defined benefit costs recognized in Other comprehensive income (loss)	(68)	27
Post-retirement benefits
Disclosure of defined benefit plans [line items]
Return on plan assets (excluding amounts included in net interest expense)	0	0
Actuarial gains (losses) arising from changes in demographic assumptions	0	2
Actuarial gains (losses) arising from changes in financial assumptions	13	(19)
Actuarial gains (losses) arising from experience adjustments	7	18
Foreign exchange rate movement	0	2
Components of defined benefit costs recognized in Other comprehensive income (loss)	$ 20	$ 3

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2021-01-01
-Paragraph 141
-Subparagraph c
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2021-en-r&anchor=para_141_c_ii&doctype=Standard
-URIDate 2021-03-24

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- Definition

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2021-01-01
-Paragraph 141
-Subparagraph c
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2021-en-r&anchor=para_141_c_iii&doctype=Standard
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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

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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 2021-01-01
-Paragraph 141
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2021-en-r&anchor=para_141_e&doctype=Standard
-URIDate 2021-03-24

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- Definition

The amount of other comprehensive income, before tax, related to gains (losses) on remeasurements of defined benefit plans, which comprise actuarial gains and losses; the return on plan assets, excluding amounts included in net interest on the net defined benefit liability (asset); and any change in the effect of the asset ceiling, excluding amounts included in net interest on the net defined benefit liability (asset). [Refer: Other comprehensive income; Defined benefit plans [member]; Plan assets [member]; Net defined benefit liability (asset)] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from gain (loss) on remeasurement in other comprehensive income]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2021-01-01
-Paragraph 135
-Subparagraph b
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-URIDate 2021-03-24

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2021-01-01
-Paragraph 91
-Subparagraph b
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-URIDate 2021-03-24

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2021-01-01
-Paragraph 7
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-URIDate 2021-03-24

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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 plan 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]; Increase (decrease) in net defined benefit liability (asset) resulting from interest expense (income)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2021-01-01
-Paragraph 141
-Subparagraph c
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2021-en-r&anchor=para_141_c_i&doctype=Standard
-URIDate 2021-03-24

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- Definition

Actuarial Gains (Losses) Arising From Experience Adjustment, Net Defined Benefit Liability (Asset)

+ References

No definition available.

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