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Pension Plans and Other Postretirement Benefit Plans - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Apr. 30, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Curtailments |  | $ 1 |  |  |  |  |
Other current liabilities |  |  | $ (15) |  | $ (14) |  |
Non-current liabilities |  |  | (75) |  | (90) |  |
Pension Plan and SERP [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Benefit obligation as of beginning of year |  |  | 585 | [1] | 558 |  |
Service cost | [2] |  | 16 |  | 14 |  | $ 24
Interest cost |  |  | $ 34 |  | $ 33 |  | 27
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] |  |  | Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses |  | Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses |  |
Actuarial (gain)/loss | [3] |  | $ 2 |  | $ 21 |  |
Benefits paid |  |  | (36) |  | (41) |  |
Curtailments |  |  | (1) |  |  |  |
Benefit obligation as of end of year |  |  | 600 | [1] | 585 | [1] | 558
Fair value of plan assets as of beginning of year |  |  | 590 | [1] | 541 |  |
Actual return on plan assets |  |  | 42 |  | 79 |  |
Employer contributions |  |  | 10 |  | 10 |  |
Benefits paid |  |  | (34) |  | (40) |  |
Fair value of plan assets as of end of year |  |  | 608 | [1] | 590 | [1] | 541
Funded status |  |  | 8 |  | 5 |  |
Other non-current assets |  |  | 35 |  | 33 |  |
Other current liabilities |  |  | (2) |  | (2) |  |
Non-current liabilities |  |  | (25) |  | (26) |  |
Net amount recognized |  |  | 8 |  | 5 |  |
Accumulated pension benefit obligation | [1] |  | 522 |  | 514 |  |
Unrecognized prior service cost (credit) |  |  | 3 |  | 4 |  |
Unrecognized net actuarial loss |  |  | 70 |  | 69 |  |
Total |  |  | 73 |  | 73 |  |
Less regulatory asset |  |  | (73) |  | (72) |  |
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans |  |  | $ 0 |  | $ 1 |  |
Discount rate for benefit obligation |  |  | 6.13% |  | 5.86% |  |
Discount rate for annual expense |  |  | 5.86% |  | 6.10% |  |
Expected long-term return on plan assets |  |  | 7.80% |  | 8.30% |  |
Rate of compensation increase |  |  | 5.19% |  | 4.87% |  |
Other Postretirement Benefits [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Benefit obligation as of beginning of year |  |  | $ 122 | [1] | $ 116 |  |
Service cost | [2] |  | 3 |  | 2 |  | 4
Interest cost |  |  | $ 7 |  | $ 7 |  | 6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] |  |  | Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses |  | Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses |  |
Actuarial (gain)/loss | [3] |  | $ (9) |  | $ 4 |  |
Benefits paid |  |  | (6) |  | (7) |  |
Benefit obligation as of end of year |  |  | 117 | [1] | 122 | [1] | 116
Fair value of plan assets as of beginning of year |  |  | 58 | [1] | 49 |  |
Actual return on plan assets |  |  | 9 |  | 9 |  |
Fair value of plan assets as of end of year |  |  | 67 | [1] | 58 | [1] | $ 49
Funded status |  |  | (50) |  | (64) |  |
Other current liabilities |  |  | (1) |  | (1) |  |
Non-current liabilities |  |  | (49) |  | (63) |  |
Net amount recognized |  |  | (50) |  | (64) |  |
Unrecognized prior service cost (credit) |  |  | 0 |  | (1) |  |
Unrecognized net actuarial loss |  |  | 2 |  | 13 |  |
Total |  |  | 2 |  | 12 |  |
Less regulatory asset |  |  | (2) |  | (13) |  |
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans |  |  | $ 0 |  | $ (1) |  |
Discount rate for benefit obligation |  |  | 6.09% |  | 5.83% |  |
Discount rate for annual expense |  |  | 5.83% |  | 6.10% |  |
Expected long-term return on plan assets |  |  | 6.70% |  | 7.20% |  |
Other Postretirement Benefits [Member] | Pre-Age 65 [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Medical cost trend – initial |  |  | 6.50% |  | 6.50% |  |
Medical cost trend – ultimate |  |  | 5.00% |  | 5.00% |  |
Ultimate medical cost trend year |  |  | 2031 |  | 2030 |  |
Other Postretirement Benefits [Member] | Post-Age 65 [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Medical cost trend – initial |  |  | 6.50% |  | 6.50% |  |
Medical cost trend – ultimate |  |  | 5.00% |  | 5.00% |  |
Ultimate medical cost trend year |  |  | 2031 |  | 2030 |  |
Other Postretirement Benefits [Member] | Retirees [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Benefit obligation as of beginning of year |  |  | $ 68 |  |  |  |
Benefit obligation as of end of year |  |  | 67 |  | $ 68 |  |
Other Postretirement Benefits [Member] | Fully eligible employees [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Benefit obligation as of beginning of year |  |  | 16 |  |  |  |
Benefit obligation as of end of year |  |  | 16 |  | 16 |  |
Other Postretirement Benefits [Member] | Other participants [Member] |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Benefit obligation as of beginning of year |  |  | 38 |  |  |  |
Benefit obligation as of end of year |  |  | $ 34 |  | $ 38 |  |
[1] | As of December 31, 2024, the SERP had a projected benefit obligation of $27 million and an accumulated benefit obligation of $26 million, with no plan assets.
[2] | Total service cost in the table above is recorded to the same accounts as labor expense. Labor and benefits expense is recorded to variou s projects based on whether the work is a capital project or an operating expense. Approximately 45 percent of all labor and benefits is capitalized to utility property and 55 percent is expensed to utility other operating expenses.
[3] | The change in the pension benefit obligation related to actuarial loss is primarily related to changes in demographic experience, partially offset by financial assumption changes.

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- Definition Accumulated other comprehensive income loss pension and other postretirement benefit plans before regulatory asset net of tax. + References No definition available. + Details
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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, after 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. + 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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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 60 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480266/715-60-50-4 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(6) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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