Leases - Summary of Components of Net Lease Cost (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Nov. 30, 2019	Nov. 30, 2019
Leases [Abstract]
Operating lease cost	[1]	$ 676	$ 1,350
Finance lease cost:
Amortization of right-of-use assets		3	6
Interest on lease liabilities		1	2
Total finance lease cost		4	8
Short-term lease cost		46	81
Variable lease cost	[1]	282	549
Net lease cost		$ 1,008	$ 1,988

[1] Expenses are primarily accounted for in the “Rentals and landing fees” line item. Additional amounts related to embedded leases are accounted for in the “Purchased transportation,” “Fuel” and “Other” line items in the unaudited condensed consolidated statements of income.