Retirement Plans - Schedule of MTM Adjustments (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
May 31, 2020 |
May 31, 2019 |
May 31, 2020 |
May 31, 2019 |
May 31, 2018 |
|
| Actuarial Gain Loss By Component Pre Tax [Abstract] | |||||
| Discount rate change | $ 2,997 | $ 1,780 | $ (613) | ||
| Demographic experience: | |||||
| Current year actuarial loss | 50 | 739 | 419 | ||
| Change in future assumptions | (229) | 887 | (37) | ||
| Actual versus expected return on assets | (2,024) | 476 | 11 | ||
| Annuity contract purchase | 210 | ||||
| Total MTM loss (gain) | $ 794 | $ 3,900 | $ 794 | $ 3,882 | $ (10) |