Financing Arrangements - Additional Information (Details)	3 Months Ended
	Aug. 31, 2020 USD ($) air-craft	May 31, 2020 USD ($)
Line Of Credit Facility [Line Items]
Number of Boeing aircraft | air-craft	19
Net book value of Boeing aircraft	$ 1,900,000,000
Letter of credit maximum sublimit amount	$ 250,000,000
Financial Covenant Terms Ratio	475.00%
Financial covenant compliance ratio	290.00%
Commercial paper outstanding	$ 0
Letters Of Credit Outstanding	300,000
Long term debt, including current maturities and exclusive of finance leases carrying value	22,800,000,000	$ 21,500,000,000
Long term debt, including current maturities and exclusive of finance leases fair value	$ 26,000,000,000.0	$ 22,800,000,000
Long-term debt weighted-average interest rate	3.50%
Five-Year Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility, term	5 years
Line of credit facility maximum borrowing capacity	$ 2,000,000,000.0
Line of credit facility, expiration date	2025-03
364-Day Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility, term	364 days
Line of credit facility maximum borrowing capacity	$ 1,500,000,000
Line of credit facility, expiration date	2021-03
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility outstanding for future borrowings	$ 3,500,000,000
1.875% due in February 2034 [Member]
Line Of Credit Facility [Line Items]
Debt instrument, face amount	$ 970,000,000
Fixed interest rate	1.875%
Debt instrument, maturity date	2034-02