Leases - Additional Information (Details) - USD ($) $ in Billions	12 Months Ended
	May 31, 2020	May 31, 2019
Lessee Lease Description [Line Items]
Finance and operating leases expiration term	various dates through 2060
Percentage total aircraft fleet leased	5.00%	6.00%
Additional leases not yet commenced, undiscounted future payments	$ 1.6
Minimum [Member]
Lessee Lease Description [Line Items]
Operating lease commencement date	2021
Maximum [Member]
Lessee Lease Description [Line Items]
Operating lease commencement date	2022