Pension and Other Postretirement Benefits (Plans with PBO in Excess of Plan Assets) (Details) - USD ($) $ in Millions |
Apr. 30, 2021 |
Apr. 30, 2020 |
Apr. 30, 2019 |
|---|---|---|---|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Total, Plan Assets | $ 836 | $ 749 | |
| Pension Plan [Member] | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation | (941) | (1,005) | |
| Defined Benefit Plan, Pension Plan with Plan Assets in Excess of Projected Benefit Obligation, Projected Benefit Obligation | (71) | 0 | |
| Defined Benefit Plan, Benefit Obligation | (1,012) | (1,005) | $ (908) |
| Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets | 761 | 749 | |
| Defined Benefit Plan, Pension Plan with Plan Assets in Excess of Projected Benefit Obligation, Plan Assets | 75 | 0 | |
| Total, Plan Assets | $ 836 | $ 749 | $ 754 |