Condensed Consolidating Financial Statements (Details 3) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2015	Aug. 31, 2014
Condensed Financial Statements Captions [Line Items]
REVENUES	$ 12,279	$ 11,684
OPERATING EXPENSES:
Salaries and employee benefits	4,525	4,114
Purchased transportation	2,344	2,054
Rentals and landing fees	695	660
Depreciation and amortization	648	651
Fuel	712	1,120
Maintenance and repairs	548	556
Other	1,663	1,467
OPERATING EXPENSES	11,135	10,622
OPERATING INCOME	1,144	1,062
OTHER INCOME (EXPENSE):
Interest, net	(63)	(48)
Other, net	3	(2)
INCOME BEFORE INCOME TAXES	1,084	1,012
PROVISION FOR INCOME TAXES	392	359
NET INCOME	692	653
COMPREHENSIVE INCOME	530	606
Parent Company Member
OPERATING EXPENSES:
Salaries and employee benefits	34	30
Rentals and landing fees	1	1
Intercompany charges, net	(69)	(95)
Other	34	64
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	692	653
Interest, net	(75)	(53)
Intercompany charges, net	78	54
Other, net	(3)	(1)
INCOME BEFORE INCOME TAXES	692	653
NET INCOME	692	653
COMPREHENSIVE INCOME	674	636
Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	9,873	9,769
OPERATING EXPENSES:
Salaries and employee benefits	3,813	3,534
Purchased transportation	1,434	1,386
Rentals and landing fees	587	572
Depreciation and amortization	583	595
Fuel	691	1,095
Maintenance and repairs	508	522
Intercompany charges, net	(40)	2
Other	1,264	1,165
OPERATING EXPENSES	8,840	8,871
OPERATING INCOME	1,033	898
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	61	98
Interest, net	8	4
Intercompany charges, net	(76)	(59)
Other, net	(3)	(3)
INCOME BEFORE INCOME TAXES	1,023	938
PROVISION FOR INCOME TAXES	357	296
NET INCOME	666	642
COMPREHENSIVE INCOME	651	638
Non Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	2,509	2,004
OPERATING EXPENSES:
Salaries and employee benefits	678	550
Purchased transportation	965	711
Rentals and landing fees	108	88
Depreciation and amortization	65	56
Fuel	21	25
Maintenance and repairs	40	34
Intercompany charges, net	109	93
Other	412	283
OPERATING EXPENSES	2,398	1,840
OPERATING INCOME	111	164
OTHER INCOME (EXPENSE):
Interest, net	4	1
Intercompany charges, net	(2)	5
Other, net	9	2
INCOME BEFORE INCOME TAXES	122	172
PROVISION FOR INCOME TAXES	35	63
NET INCOME	87	109
COMPREHENSIVE INCOME	(42)	83
Consolidation Eliminations Member
Condensed Financial Statements Captions [Line Items]
REVENUES	(103)	(89)
OPERATING EXPENSES:
Purchased transportation	(55)	(43)
Rentals and landing fees	(1)	(1)
Other	(47)	(45)
OPERATING EXPENSES	(103)	(89)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(753)	(751)
INCOME BEFORE INCOME TAXES	(753)	(751)
NET INCOME	(753)	(751)
COMPREHENSIVE INCOME	$ (753)	$ (751)