Retirement Plans - Schedule of Retirement Plan Costs (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
May 31, 2021 |
May 31, 2020 |
May 31, 2019 |
|
| Pension And Other Postretirement Benefit Expense [Abstract] | |||
| Defined benefit pension plans | $ 88 | $ 148 | $ 112 |
| Defined contribution plans | 685 | 574 | 561 |
| Postretirement healthcare plans | 83 | 86 | 75 |
| Retirement plans MTM (gain) loss | (1,176) | 794 | 3,882 |
| Retirement plans costs | $ (320) | $ 1,602 | $ 4,630 |