Pension and Other Postretirement Benefits (Schedule of Components of Pension Expense) (Details) - Pension Benefits [Member] - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Apr. 30, 2021 |
Apr. 30, 2020 |
Apr. 30, 2019 |
|
| Pension Expense | |||
| Service cost | $ 26 | $ 24 | $ 24 |
| Interest cost | 25 | 31 | 34 |
| Expected return on assets | (46) | (46) | (47) |
| Amortization of prior service cost (credit) | 1 | 1 | 1 |
| Amortization of net actuarial loss (gain) | 27 | 19 | 19 |
| Settlement charge | 0 | 1 | 15 |
| Net cost | $ 33 | $ 30 | $ 46 |