Employee Benefit Plans - Schedule of Pension Plans with a Benefit Obligation in Excess of Plan Assets (Details) - USD ($) $ in Millions |
Sep. 30, 2021 |
Sep. 30, 2020 |
|---|---|---|
| Plans with projected benefit obligation in excess of plan assets | ||
| Plans with projected benefit obligation in excess of plan assets, benefit obligation | $ 1,607 | $ 2,275 |
| Plans with projected benefit obligation in excess of plan assets, plan assets | 1,386 | 1,998 |
| Plans with accumulated benefit obligation in excess of plan assets | ||
| Plans with accumulated benefit obligation in excess of plan assets, benefit obligation | 1,593 | 2,253 |
| Plans with accumulated benefit obligation in excess of plan assets, plan assets | $ 1,374 | $ 1,978 |