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Employee Future Benefits - Components Recognized in OCI and Regulatory Assets (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
DBP Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Current year net actuarial (gains) losses	$ (1)	$ 4
Past service credits/plan amendments	0	0
Foreign currency translation	0	(1)
Income tax recovery	0	(1)
Total recognized in comprehensive income	(1)	2
Regulatory Assets, Pension and Other Postretirement Benefit Plans [Abstract]
Current year net actuarial (gains) losses	(142)	78
Amortization of actuarial gains	1	9
Amortization of past service credits	1	2
Foreign currency translation	(2)	(1)
Regulatory adjustments	23	(5)
Total recognized in regulatory (liabilities) assets	(119)	83
OPEB Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Current year net actuarial (gains) losses	(1)	1
Past service credits/plan amendments	0	(1)
Foreign currency translation	0	0
Income tax recovery	0	0
Total recognized in comprehensive income	(1)	0
Regulatory Assets, Pension and Other Postretirement Benefit Plans [Abstract]
Current year net actuarial (gains) losses	(72)	(40)
Amortization of actuarial gains	16	18
Amortization of past service credits	1	1
Foreign currency translation	(12)	2
Regulatory adjustments	2	(5)
Total recognized in regulatory (liabilities) assets	$ (65)	$ (24)

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Regulatory Assets, Amortization Adjustment, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit)

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Regulatory Assets, Pension and Other Postretirement Benefit Plans, Adjustment

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Regulatory Assets, Pension and Other Postretirement Benefit Plans, Foreign Currency Gain (Loss)

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Regulatory Assets, Pension and Other Postretirement Benefit Plans, Net Actuarial Gain (Loss) Arising During Period

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Regulatory Assets, Reclassification Adjustment, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss)

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan.

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