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Benefit Plans Contributions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure
Defined contribution plan contribution amount		$ 97	$ 92	$ 88
Other postretirement benefit contributions		28	25
Contribution related to TVARS case		4	5
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure
Defined Benefit Plan, Related to SERP		8	6
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Employer contributions		28	27
Pension Benefits
Defined Benefit Plan Disclosure
Employer contributions		308	$ 306
Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		300
Minimum | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		$ 300
Scenario, Forecast
Defined Benefit Plan Disclosure
Defined contribution plan contribution amount	$ 101
Scenario, Forecast | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions	$ 300

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

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