Retirement Plans - Schedule of MTM Adjustments (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Actuarial Gain Loss By Component Pre Tax [Abstract]
Actual versus expected return on assets	$ (1,712)	$ (2,024)	$ 476
Discount rate change	(397)	2,997	1,780
Demographic experience:
Current year actuarial loss	302	50	739
Change in future assumptions	685	(229)	887
Curtailment gain on TNT Netherlands pension plan	(54)
Total MTM (gain) loss	$ (1,176)	$ 794	$ 3,882