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Pensions and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 5 Months Ended | 9 Months Ended
--- | --- | --- | ---
Jun. 30, 2024 | May 31, 2024 | Sep. 30, 2024 | Sep. 30, 2023
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Curtailment gain |  | $ 0 | $ 0 | $ 0
Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Curtailment gain | $ 20 |  | $ 20 | $ 0
Percent reduction in future years of service of plan participants (as a percent) |  | 10.00% |  |
Benefit obligation discount rate (as a percent) |  | 5.74% |  |
Reduction to benefit obligation |  | $ 11 |  |

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation 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 Amount of (increase) decrease in benefit obligation of defined benefit plan from event reducing expected years of future service of present employees or eliminating accrual of benefits for some or all future services of present employees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(10) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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