Benefit Plans Sensitivity to Certain Changes in Pension Assumptions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	0.25%
Discount rate		5.00%	6.05%
Discount rate
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 12,000,000
Impact on Projected Benefit Obligation	$ 241,000,000
Rate of return on plan assets
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 19,000,000
Cost of Living Adjustments [Domain]
Defined Benefit Plan Disclosure
Change in Assumption	0.25%
Impact on Pension Cost	$ 20,000,000
Impact on Projected Benefit Obligation	$ 168,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Discount rate	5.62%	5.00%
Actuarial assumption COLA	$ 0.0277	$ 0.0444	$ 0.06
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
COLA percentage increase (decrease)	6.00%
Discount rate	5.47%	4.95%	5.95%