Employee Future Benefits - Pension and Retiree Welfare Plans (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Pension plans
Disclosure of defined benefit plans [line items]
Opening balance, January 1	$ 50
Return on plan assets (excluding interest income)	27	$ (31)
Actuarial losses (gains) due to:
Experience	(17)	2
Demographic assumption changes	(24)	0
Economic assumption changes	19	(101)
Defined benefit obligation, December 31	5	50
Pension plans \| Present value of defined benefit obligation
Disclosure of defined benefit plans [line items]
Opening balance, January 1	3,826	3,789
Current service cost	44	44
Past service cost – amendment	0	0
Interest cost	184	176
Plan participants’ contributions	0	0
Actuarial losses (gains) due to:
Experience	(17)	2
Demographic assumption changes	(24)	0
Economic assumption changes	19	(101)
Benefits paid	314	303
Impact of changes in foreign exchange rates	(116)	219
Defined benefit obligation, December 31	3,602	3,826
Pension plans \| Plan assets
Disclosure of defined benefit plans [line items]
Opening balance, January 1	(3,820)	(3,706)
Interest cost	(188)	(174)
Plan participants’ contributions	0	0
Return on plan assets (excluding interest income)	27	(31)
Employer contributions	55	57
Actuarial losses (gains) due to:
Benefits paid	(314)	(303)
Impact of changes in foreign exchange rates	123	(225)
Administration costs	(10)	(8)
Defined benefit obligation, December 31	(3,643)	(3,820)
Retiree welfare plans
Disclosure of defined benefit plans [line items]
Opening balance, January 1	(125)
Return on plan assets (excluding interest income)	13	(19)
Actuarial losses (gains) due to:
Experience	(10)	(16)
Demographic assumption changes	(6)	0
Economic assumption changes	(3)	(19)
Defined benefit obligation, December 31	(166)	(125)
Retiree welfare plans \| Present value of defined benefit obligation
Disclosure of defined benefit plans [line items]
Opening balance, January 1	428	450
Current service cost	0	0
Past service cost – amendment	0	0
Interest cost	21	21
Plan participants’ contributions	2	2
Actuarial losses (gains) due to:
Experience	(10)	(16)
Demographic assumption changes	(6)	0
Economic assumption changes	(3)	(19)
Benefits paid	37	40
Impact of changes in foreign exchange rates	(16)	30
Defined benefit obligation, December 31	379	428
Retiree welfare plans \| Plan assets
Disclosure of defined benefit plans [line items]
Opening balance, January 1	(553)	(526)
Interest cost	(29)	(26)
Plan participants’ contributions	2	2
Return on plan assets (excluding interest income)	13	(19)
Employer contributions	13	12
Actuarial losses (gains) due to:
Benefits paid	(37)	(40)
Impact of changes in foreign exchange rates	26	(48)
Administration costs	(2)	(2)
Defined benefit obligation, December 31	$ (545)	$ (553)

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 2025-01-01
-Paragraph 141
-Subparagraph c
-Clause ii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_c_ii&doctype=Standard
-URIDate 2025-03-27