Benefit Plans Estimated Future Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 827
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	826
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	826
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	819
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	808
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	3,885
Employer contributions	310	$ 304
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	17
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	17
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	16
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	16
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	16
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	93
Employer contributions	24	$ 22
SERP
Defined Benefit Plan Disclosure
Employer contributions	$ 9