Leases - Summary of Components of Net Lease Cost (Details) $ in Millions	12 Months Ended
	May 31, 2020 USD ($)
Leases [Abstract]
Operating lease cost	$ 2,668	[1]
Finance lease cost:
Amortization of right-of-use assets	18
Interest on lease liabilities	12
Total finance lease cost	30
Short-term lease cost	197
Variable lease cost	1,160	[1]
Net lease cost	$ 4,055

[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 accompanying consolidated statements of income.