Retirement Plans - Schedule of MTM Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018	May 31, 2017
Actuarial Gain Loss By Component Pre Tax [Abstract]
Discount rate change			$ 1,780	$ (613)	$ 266
Demographic experience:
Current year actuarial loss			739	419	268
Change in future assumptions			887	(37)	182
Actual versus expected return on assets			476	11	(740)
Annuity contract purchase				210
Total mark-to-market loss (gain)	$ 3,900	$ (10)	$ 3,882	$ (10)	$ (24)