Employee Benefit Plans - Schedule of Future Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 2,200	$ 2,300
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
2022	145
2023	145
2024	141
2025	139
2026	138
2027 - 2031	651
Total	1,359
Employer contributions	14	22
Accumulated benefit obligations	2,203	2,321	$ 2,287
Expected future contribution	12
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
2022	5
2023	4
2024	4
2025	3
2026	3
2027 - 2031	14
Total	33
Employer contributions	5	6
Accumulated benefit obligations	49	52	$ 55
Other various benefit plans
Defined Benefit Plan Disclosure [Line Items]
Noncurrent postemployment benefits liability	$ 3	$ 3