Condensed Consolidating Financial Statements (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Condensed Financial Statements Captions [Line Items]
REVENUES	$ 11,024	$ 10,792
OPERATING EXPENSES:
Salaries and employee benefits	4,077	4,103
Purchased transportation	1,879	1,680
Rentals and landing fees	640	618
Depreciation and amortization	639	573
Fuel	1,104	1,138
Maintenance and repairs	480	542
Other	1,410	1,396
OPERATING EXPENSES	10,229	10,050
OPERATING INCOME	795	742
OTHER INCOME (EXPENSE):
Interest, net	(27)	(10)
Other, net	(2)	(5)
INCOME BEFORE INCOME TAXES	766	727
PROVISION FOR INCOME TAXES	277	268
NET INCOME	489	459
COMPREHENSIVE INCOME	452	565
Parent Company Member
OPERATING EXPENSES:
Salaries and employee benefits	31	30
Rentals and landing fees	1	1
Intercompany charges, net	(61)	(60)
Other	29	29
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	489	459
Interest, net	(34)	(23)
Intercompany charges, net	35	24
Other, net	(1)	(1)
INCOME BEFORE INCOME TAXES	489	459
NET INCOME	489	459
COMPREHENSIVE INCOME	528	518
Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	9,228	9,094
OPERATING EXPENSES:
Salaries and employee benefits	3,514	3,589
Purchased transportation	1,242	1,130
Rentals and landing fees	558	544
Depreciation and amortization	589	530
Fuel	1,081	1,116
Maintenance and repairs	449	515
Intercompany charges, net	(6)	(112)
Other	1,133	1,133
OPERATING EXPENSES	8,560	8,445
OPERATING INCOME	668	649
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	110	29
Interest, net	5	11
Intercompany charges, net	(41)	(29)
Other, net	(2)	(2)
INCOME BEFORE INCOME TAXES	740	658
PROVISION FOR INCOME TAXES	232	236
NET INCOME	508	422
COMPREHENSIVE INCOME	507	428
Non Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	1,878	1,778
OPERATING EXPENSES:
Salaries and employee benefits	532	484
Purchased transportation	673	583
Rentals and landing fees	82	75
Depreciation and amortization	50	43
Fuel	23	22
Maintenance and repairs	31	27
Intercompany charges, net	67	172
Other	293	279
OPERATING EXPENSES	1,751	1,685
OPERATING INCOME	127	93
OTHER INCOME (EXPENSE):
Interest, net	2	2
Intercompany charges, net	6	5
Other, net	1	(2)
INCOME BEFORE INCOME TAXES	136	98
PROVISION FOR INCOME TAXES	45	32
NET INCOME	91	66
COMPREHENSIVE INCOME	16	107
Consolidation Eliminations Member
Condensed Financial Statements Captions [Line Items]
REVENUES	(82)	(80)
OPERATING EXPENSES:
Purchased transportation	(36)	(33)
Rentals and landing fees	(1)	(2)
Other	(45)	(45)
OPERATING EXPENSES	(82)	(80)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(599)	(488)
INCOME BEFORE INCOME TAXES	(599)	(488)
NET INCOME	(599)	(488)
COMPREHENSIVE INCOME	$ (599)	$ (488)