Summary of Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
May 31, 2019 |
[1] | Feb. 28, 2019 |
[1] | Nov. 30, 2018 |
[1] | Aug. 31, 2018 |
[1] | May 31, 2018 |
[2] | Feb. 28, 2018 |
[2] | Nov. 30, 2017 |
[2] | Aug. 31, 2017 |
[2] | May 31, 2019 |
May 31, 2018 |
May 31, 2017 |
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| Selected Quarterly Financial Information [Abstract] | ||||||||||||||||||||||||||||||||||||||||||
| Revenues | $ 17,807 | $ 17,010 | $ 17,824 | $ 17,052 | $ 17,314 | $ 16,526 | $ 16,313 | $ 15,297 | $ 69,693 | [3] | $ 65,450 | [3],[4] | $ 60,319 | [3],[4] | ||||||||||||||||||||||||||||
| Operating income | 1,316 | 911 | 1,168 | 1,071 | 1,328 | 858 | 1,115 | 971 | 4,466 | [5] | 4,272 | [6] | 4,566 | [7] | ||||||||||||||||||||||||||||
| Net income | $ (1,969) | [8] | $ 739 | [8] | $ 935 | [8] | $ 835 | [8] | $ 1,127 | [9] | $ 2,074 | [9] | $ 775 | [9] | $ 596 | [9] | $ 540 | $ 4,572 | $ 2,997 | |||||||||||||||||||||||
| Basic earnings per common share | $ (7.56) | [10] | $ 2.83 | [10] | $ 3.56 | [10] | $ 3.15 | [10] | $ 4.23 | [10] | $ 7.74 | [10] | $ 2.89 | [10] | $ 2.22 | [10] | $ 2.06 | $ 17.08 | $ 11.24 | |||||||||||||||||||||||
| Diluted earnings per common share | $ (7.56) | [10] | $ 2.80 | [10] | $ 3.51 | [10] | $ 3.10 | [10] | $ 4.15 | [10] | $ 7.59 | [10] | $ 2.84 | [10] | $ 2.19 | [10] | $ 2.03 | $ 16.79 | $ 11.07 | |||||||||||||||||||||||
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