Condensed Consolidating Financial Statements (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011	Nov. 30, 2010
Condensed Financial Statements Captions [Line Items]
REVENUES	$ 10,587	$ 9,632	$ 21,108	$ 19,089
OPERATING EXPENSES:
Salaries and employee benefits	3,982	3,779	7,986	7,582
Purchased transportation	1,576	1,390	3,094	2,717
Rentals and landing fees	623	628	1,243	1,229
Depreciation and amortization	518	502	1,027	981
Fuel	1,200	938	2,444	1,825
Maintenance and repairs	511	473	1,062	990
Impairment and other charges		67		67
Other	1,397	1,386	2,735	2,601
OPERATING EXPENSES	9,807	9,163	19,591	17,992
OPERATING INCOME	780	469	1,517	1,097
OTHER INCOME (EXPENSE):
Interest, net	(7)	(23)	(18)	(41)
Other, net	4	(9)	2	(16)
INCOME BEFORE INCOME TAXES	777	437	1,501	1,040
PROVISION FOR INCOME TAXES	280	154	540	377
NET INCOME	497	283	961	663
Parent Company Member
OPERATING EXPENSES:
Salaries and employee benefits	28	26	61	64
Rentals and landing fees	1	1	2	2
Depreciation and amortization	1		1
Intercompany charges, net	(53)	(58)	(111)	(129)
Other	23	31	47	63
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	497	283	961	663
Interest, net	(19)	(23)	(39)	(47)
Intercompany charges, net	21	28	42	55
Other, net	(2)	(5)	(3)	(8)
INCOME BEFORE INCOME TAXES	497	283	961	663
NET INCOME	497	283	961	663
Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	9,001	8,002	18,008	15,895
OPERATING EXPENSES:
Salaries and employee benefits	3,506	3,216	7,037	6,465
Purchased transportation	1,122	970	2,202	1,890
Rentals and landing fees	557	564	1,112	1,101
Depreciation and amortization	480	443	951	875
Fuel	1,181	891	2,405	1,732
Maintenance and repairs	486	440	1,014	923
Impairment and other charges		17		17
Intercompany charges, net	(135)	(80)	(225)	(172)
Other	1,156	1,137	2,281	2,123
OPERATING EXPENSES	8,353	7,598	16,777	14,954
OPERATING INCOME	648	404	1,231	941
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	80	23	151	49
Interest, net	11	1	19	9
Intercompany charges, net	(27)	(34)	(55)	(69)
Other, net	(1)	(3)	(3)	(7)
INCOME BEFORE INCOME TAXES	711	391	1,343	923
PROVISION FOR INCOME TAXES	202	138	417	334
NET INCOME	509	253	926	589
Non Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	1,660	1,718	3,244	3,364
OPERATING EXPENSES:
Salaries and employee benefits	448	537	888	1,053
Purchased transportation	482	447	946	879
Rentals and landing fees	67	64	132	128
Depreciation and amortization	37	59	75	106
Fuel	19	47	39	93
Maintenance and repairs	25	33	48	67
Impairment and other charges		50		50
Intercompany charges, net	188	138	336	301
Other	262	278	494	531
OPERATING EXPENSES	1,528	1,653	2,958	3,208
OPERATING INCOME	132	65	286	156
OTHER INCOME (EXPENSE):
Interest, net	1	(1)	2	(3)
Intercompany charges, net	6	6	13	14
Other, net	7	(1)	8	(1)
INCOME BEFORE INCOME TAXES	146	69	309	166
PROVISION FOR INCOME TAXES	78	16	123	43
NET INCOME	68	53	186	123
Consolidation Eliminations Member
Condensed Financial Statements Captions [Line Items]
REVENUES	(74)	(88)	(144)	(170)
OPERATING EXPENSES:
Purchased transportation	(28)	(27)	(54)	(52)
Rentals and landing fees	(2)	(1)	(3)	(2)
Other	(44)	(60)	(87)	(116)
OPERATING EXPENSES	(74)	(88)	(144)	(170)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(577)	(306)	(1,112)	(712)
INCOME BEFORE INCOME TAXES	(577)	(306)	(1,112)	(712)
NET INCOME	$ (577)	$ (306)	$ (1,112)	$ (712)