Description of Business and Summary of Significant Accounting Policies - Schedule of Depreciable Lives and Net Book Value of Our Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2017	May 31, 2016
Property Plant And Equipment [Line Items]
Net property and equipment	$ 25,981	$ 24,284
Wide Body Aircraft and Related Equipment [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	15 to 30 years
Net property and equipment	$ 9,103	8,356
Narrow Body and Feeder Aircraft and Related Equipment [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	5 to 18 years
Net property and equipment	$ 3,099	3,180
Package Handling and Ground Support Equipment [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	3 to 30 years
Net property and equipment	$ 3,862	3,249
Information Technology [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	2 to 10 years
Net property and equipment	$ 1,114	1,051
Vehicles [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	3 to 15 years
Net property and equipment	$ 3,400	3,084
Facilities and Other Property [Member]
Property Plant And Equipment [Line Items]
Depreciable lives range	2 to 40 years
Net property and equipment	$ 5,403	$ 5,364