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)