Retirement Plans - Schedule of Retirement Plan Costs (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Nov. 30, 2020 |
Nov. 30, 2019 |
Nov. 30, 2020 |
Nov. 30, 2019 |
|
| Pension And Other Postretirement Benefit Expense [Abstract] | ||||
| Defined benefit pension plans, net | $ 27 | $ 37 | $ 52 | $ 74 |
| Defined contribution plans | 153 | 136 | 311 | 278 |
| Postretirement healthcare plans | 20 | 21 | 41 | 43 |
| Retirement plan mark-to-market (“MTM”) net loss | 52 | 52 | ||
| Retirement plans costs | $ 252 | $ 194 | $ 456 | $ 395 |