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Benefit Plans and Other Postretirement Benefits - Narrative (Details) $ in Millions | 12 Months Ended |
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Dec. 31, 2023 USD ($) benefitPlan | Dec. 31, 2022 USD ($) | Nov. 01, 2023
Benefit Plans and Other Postretirement Benefits |  |  |
Number of qualified pension plans | benefitPlan | 3 |  |
STP |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Ownership percentage | 44.00% |  | 44.00%
Pension Benefits |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Expects to contribute to the pension plans | $ 43 |  |
Actuarial gain (loss) | (22) | $ 289 |
Pension Benefits | GenOn |  |  |
Benefit Plans and Other Postretirement Benefits |  |  |
Expects to contribute to the pension plans | $ 23 |  |

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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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