Benefit Plans Components of Benefit Plans (Details) - USD ($)	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2026
Defined Benefit Plan Disclosure
Fixed and variable fund annual maximum contribution	$ 10,000
Defined contribution plan contribution amount	124,000,000	$ 116,000,000	$ 105,000,000
Nonqualified Excess 401(k) Plan	2,000,000	1,000,000	$ 1
Accounts Payable and Accrued Liabilities, Current	3,299,000,000	$ 2,910,000,000
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience	37,000,000
Actuarial Gain (Loss) from Changes in Mortality Assumptions	5,000,000
Actuarial Gain (Loss) from pre-Medicare Trend Rate Assumptions	30,000,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Discount rate		5.00%	6.05%
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption		$ 46,000,000
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions	18,000,000
Actuarial Gain (Loss) due to Adoption of a Retiree Persistency Assumption	13,000,000
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience	37,000,000
Accounts payable and accrued liabilities
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Postemployment Benefits Liability		28,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Accounts Payable and Accrued Liabilities, Current	$ 17,000,000	$ 20,000,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Discount rate	5.62%	5.00%
Actuarial Gain (Loss) from Delaying post-Medicare Trend Rate Assumption	$ 28,000,000
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions	3,000,000
Pension Benefits
Defined Benefit Plan Disclosure
Accounts Payable and Accrued Liabilities, Current	9,000,000	$ 6,000,000
Amount of defined benefit plan actuarial gain (loss) from discount rate change	514,000,000	$ 981,000,000
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience	$ 18,000,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Discount rate	5.47%	4.95%	5.95%
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption	$ 39,000,000
Actual Return on Plan Assets	4.90%	12.72%	6.13%
Amount of defined benefit plan actuarial gain (loss) from change in demograhic and plan experience	$ 18,000,000
Minimum
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	300.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	150.00%
Maximum
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	600.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	600.00%
Minimum
Defined Benefit Plan Disclosure
Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach	10.00%
Scenario, Forecast | Pension Benefits
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate [Abstract]
Defined Benefit Plan, Cost of Living Adjustment Assumption Next Fiscal Year				2.49%