Retirement Plans - Narratives (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan, projected benefit obligation (ABO)	$ 162	$ 155
Pension plan, accumulated benefit obligation (ABO)	144	137
Pension plan, fair value of plan assets (ABO)	52	48
Pension plan, projected benefit obligation (PBO)	162	155
Pension plan, accumulated benefit obligation (PBO)	144	137
Pension plan, fair value of plan assets (PBO)	52	48
Amounts in AOCI	2	2
Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, contributions	20	17
Expected contributions in the next fiscal year	10
Savings and investment plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution expense	$ 38	$ 46	$ 23

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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