Employee Future Benefits - Amounts Recognized in Consolidated Statements of Financial Position (Detail) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Pension plans
Disclosure of defined benefit plans [line items]
Defined benefit obligation	$ 3,826	$ 3,789
Fair value of plan assets	3,820	3,706
Deficit (surplus)	6	83
Effect of asset limit	44	41
Deficit (surplus) and net defined benefit liability (asset)	50	124
Pension plans \| Funded or partially funded plans
Disclosure of defined benefit plans [line items]
Deficit (surplus) and net defined benefit liability (asset)	(483)	(422)
Pension plans \| Unfunded plans
Disclosure of defined benefit plans [line items]
Deficit (surplus) and net defined benefit liability (asset)	533	546
Retiree welfare plans
Disclosure of defined benefit plans [line items]
Defined benefit obligation	428	450
Fair value of plan assets	553	526
Deficit (surplus)	(125)	(76)
Effect of asset limit	0	0
Deficit (surplus) and net defined benefit liability (asset)	(125)	(76)
Retiree welfare plans \| Funded or partially funded plans
Disclosure of defined benefit plans [line items]
Deficit (surplus) and net defined benefit liability (asset)	(221)	(190)
Retiree welfare plans \| Unfunded plans
Disclosure of defined benefit plans [line items]
Deficit (surplus) and net defined benefit liability (asset)	$ 96	$ 114

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 57
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_57_a&doctype=Standard
-URIDate 2024-03-27

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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 decrease (increase) in the net defined benefit liability (asset) resulting from the gain (loss) on changes in the effect of limiting a net defined benefit asset to the asset ceiling, excluding amounts included in interest income or expense. [Refer: Interest income (expense); Net defined benefit liability (asset); 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 2024-01-01
-Paragraph 141
-Subparagraph c
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_c_iv&doctype=Standard
-URIDate 2024-03-27

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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 [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 140
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_140_a&doctype=Standard
-URIDate 2024-03-27

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- Definition

The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

+ References

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- Definition

The fair value of any plan assets, less the present value of the defined benefit obligation. [Refer: Plan assets [member]]

+ References

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