Summary of Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
May 31, 2020 |
[1] | Feb. 29, 2020 |
[1] | Nov. 30, 2019 |
[1] | Aug. 31, 2019 |
[1] | May 31, 2019 |
[2] | Feb. 28, 2019 |
[2] | Nov. 30, 2018 |
[2] | Aug. 31, 2018 |
[2] | May 31, 2020 |
May 31, 2019 |
May 31, 2018 |
||||||||||||||||||||||||
| Selected Quarterly Financial Information [Abstract] | ||||||||||||||||||||||||||||||||||||||||||
| Revenues | $ 17,358 | $ 17,487 | $ 17,324 | $ 17,048 | $ 17,807 | $ 17,010 | $ 17,824 | $ 17,052 | $ 69,217 | [3] | $ 69,693 | [3],[4] | $ 65,450 | [3],[4] | ||||||||||||||||||||||||||||
| Operating income | 475 | 411 | 554 | 977 | 1,316 | 911 | 1,168 | 1,071 | 2,417 | [5] | 4,466 | [6] | 4,272 | [7] | ||||||||||||||||||||||||||||
| Net income | $ (334) | [8] | $ 315 | [8] | $ 560 | [8] | $ 745 | [8] | $ (1,969) | [9] | $ 739 | [9] | $ 935 | [9] | $ 835 | [9] | $ 1,286 | $ 540 | $ 4,572 | |||||||||||||||||||||||
| Basic earnings (loss) per common share | $ (1.28) | [10] | $ 1.21 | [10] | $ 2.15 | [10] | $ 2.86 | [10] | $ (7.56) | [10] | $ 2.83 | [10] | $ 3.56 | [10] | $ 3.15 | [10] | $ 4.92 | $ 2.06 | $ 17.08 | |||||||||||||||||||||||
| Diluted earnings (loss) per common share | $ (1.28) | [10] | $ 1.20 | [10] | $ 2.13 | [10] | $ 2.84 | [10] | $ (7.56) | [10] | $ 2.80 | [10] | $ 3.51 | [10] | $ 3.10 | [10] | $ 4.90 | $ 2.03 | $ 16.79 | |||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||||