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Benefit Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Pension Benefits |  |  |
Defined Benefit Plan Disclosure |  |  |
Service cost | $ 32 | $ 53 | $ 57
DefinedBenefitPlanNetPeriodicBenefitCostCreditInterestCostStatementOfIncome | 568 | 378 | 368
DefinedBenefitPlanNetPeriodicBenefitCostCreditExpectedReturnLossStatementOfIncome | (492) | (435) | (493)
DefinedBenefitPlanNetPeriodicBenefitCostCreditAmortizationOfPriorServiceCostCreditStatementOfIncome | (88) | (93) | (97)
DefinedBenefitPlanNetPeriodicBenefitCostCreditAmortizationOfGainLossStatementOfIncome | 135 | 392 | 452
Net periodic benefit cost as acutarially determined | 155 | 295 | 287
Amount expensed due to actions of regulator | (77) | (13) | (19)
Total net period benefit cost | 232 | 308 | 306
Other Post-retirement Benefits |  |  |
Defined Benefit Plan Disclosure |  |  |
Service cost | 10 | 17 | 18
DefinedBenefitPlanNetPeriodicBenefitCostCreditInterestCostStatementOfIncome | 18 | 15 | 16
Expected return on plan assets | 0 | 0 | 0
DefinedBenefitPlanNetPeriodicBenefitCostCreditAmortizationOfPriorServiceCostCreditStatementOfIncome | (17) | (17) | (18)
DefinedBenefitPlanNetPeriodicBenefitCostCreditAmortizationOfGainLossStatementOfIncome | (2) | (5) | (11)
Net periodic benefit cost as acutarially determined | 9 | 20 | 27
Amount expensed due to actions of regulator | 0 | 0 | 0
Total net period benefit cost | $ 9 | $ 20 | $ 27

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- Definition The total amount of net periodic benefit cost actuarilly determined for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. + References No definition available. + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + 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 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: 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 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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