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Employee Future Benefits - Components of AOCI and Regulatory Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Pension and Other Postretirement Benefit Plans, Net Regulatory Assets [Abstract]
Regulatory assets (Note 8)	$ 4,631	$ 4,384
Regulatory liabilities (Note 8)	(4,291)	(3,958)
DBP Plans
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Unamortized net actuarial losses (gains)	11	12
Unamortized past service costs	1	1
Income tax (recovery) expense	(3)	(3)
Accumulated other comprehensive income	9	10
Pension and Other Postretirement Benefit Plans, Net Regulatory Assets [Abstract]
Net actuarial losses (gains)	46	189
Past service credits	(1)	(2)
Other regulatory deferrals	12	(11)
Regulatory assets (Note 8)	235	254
Regulatory liabilities (Note 8)	(178)	(78)
Net regulatory assets (liabilities)	57	176
OPEB Plans
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Unamortized net actuarial losses (gains)	(11)	(10)
Unamortized past service costs	6	6
Income tax (recovery) expense	1	1
Accumulated other comprehensive income	(4)	(3)
Pension and Other Postretirement Benefit Plans, Net Regulatory Assets [Abstract]
Net actuarial losses (gains)	(283)	(215)
Past service credits	(2)	(3)
Other regulatory deferrals	4	2
Regulatory assets (Note 8)	0	0
Regulatory liabilities (Note 8)	(281)	(216)
Net regulatory assets (liabilities)	$ (281)	$ (216)

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Pension and Other Postretirement Benefit Plans, Net Regulatory Assets, Amount Deferred Due to Actions of Regulators

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Pension and Other Postretirement Benefit Plans, Net Regulatory Assets, Net Gains (Losses)

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

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Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for 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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The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

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