Retirement Plans - Narratives (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan, projected benefit obligation (ABO)	$ 155	$ 162
Pension plan, accumulated benefit obligation (ABO)	135	144
Pension plan, fair value of plan assets (ABO)	38	52
Amounts in AOCI	2	2
Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, contributions	18	20
Expected contributions in the next fiscal year	8
Savings and investment plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution expense	$ 43	$ 38	$ 46

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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