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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
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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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- Definition Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-14A Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (j) -SubTopic 10 -Topic 220 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (k) -SubTopic 10 -Topic 220 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (j) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-14A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (j) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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