Benefit Plans Contributions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure
Defined contribution plan contribution amount		$ 124	$ 116	$ 105
Other postretirement benefit contributions		24	22
Contribution related to TVARS case		5	5
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure
Defined Benefit Plan, Related to SERP		10	4
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Employer contributions		24	22
Pension Benefits
Defined Benefit Plan Disclosure
Employer contributions		310	$ 304
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 | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions	$ 300