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Employee Future Benefits - Components Recognized in OCI and Regulatory Assets (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Pension Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Current year net actuarial losses (gains)	$ 4	$ (23)
Past service cost/plan amendments	0	0
Amortization of actuarial losses	0	1
Foreign currency translation	(1)	(2)
Income tax (recovery) expense	(1)	6
Total recognized in comprehensive income	2	(18)
Regulatory Assets, Pension and Other Postretirement Benefit Plans [Abstract]
Current year net actuarial losses (gains)	78	(155)
Past service cost/plan amendments	0	0
Amortization of actuarial gains (losses)	9	(6)
Amortization of past service credits	2	1
Foreign currency translation	(1)	4
Regulatory adjustments	(5)	(16)
Total recognized in regulatory assets (liabilities)	83	(172)
OPEB Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Current year net actuarial losses (gains)	1	(6)
Past service cost/plan amendments	(1)	0
Amortization of actuarial losses	0	0
Foreign currency translation	0	0
Income tax (recovery) expense	0	1
Total recognized in comprehensive income	0	(5)
Regulatory Assets, Pension and Other Postretirement Benefit Plans [Abstract]
Current year net actuarial losses (gains)	(40)	(118)
Past service cost/plan amendments	0	1
Amortization of actuarial gains (losses)	18	10
Amortization of past service credits	1	1
Foreign currency translation	2	(6)
Regulatory adjustments	(5)	(7)
Total recognized in regulatory assets (liabilities)	$ (24)	$ (119)

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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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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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