Condensed Consolidating Financial Statements (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014
Condensed Financial Statements Captions [Line Items]
REVENUES	$ 11,716	$ 11,301	$ 35,339	$ 33,728
OPERATING EXPENSES:
Salaries and employee benefits	4,411	4,167	12,904	12,392
Purchased transportation	2,165	2,063	6,404	5,982
Rentals and landing fees	686	662	2,009	1,950
Depreciation and amortization	652	652	1,954	1,938
Fuel	810	1,163	2,982	3,403
Maintenance and repairs	505	438	1,604	1,397
Other	1,525	1,515	4,520	4,403
OPERATING EXPENSES	10,754	10,660	32,377	31,465
OPERATING INCOME	962	641	2,962	2,263
OTHER INCOME (EXPENSE):
Interest, net	(58)	(38)	(153)	(95)
Other, net	5	(9)	8	(16)
INCOME BEFORE INCOME TAXES	909	594	2,817	2,152
PROVISION FOR INCOME TAXES	329	216	1,015	785
NET INCOME	580	378	1,802	1,367
COMPREHENSIVE INCOME	458	393	1,587	1,433
Parent Company Member
OPERATING EXPENSES:
Salaries and employee benefits	25	24	78	79
Rentals and landing fees	1	1	4	4
Depreciation and amortization			1	1
Maintenance and repairs		1		1
Intercompany charges, net	(48)	(52)	(191)	(163)
Other	22	26	108	78
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	580	378	1,802	1,367
Interest, net	(66)	(45)	(172)	(114)
Intercompany charges, net	68	46	176	117
Other, net	(2)	(1)	(4)	(3)
INCOME BEFORE INCOME TAXES	580	378	1,802	1,367
NET INCOME	580	378	1,802	1,367
COMPREHENSIVE INCOME	607	419	1,883	1,487
Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	9,793	9,509	29,488	28,184
OPERATING EXPENSES:
Salaries and employee benefits	3,784	3,615	11,119	10,697
Purchased transportation	1,527	1,426	4,381	4,008
Rentals and landing fees	597	576	1,746	1,697
Depreciation and amortization	593	601	1,783	1,785
Fuel	790	1,138	2,913	3,330
Maintenance and repairs	468	406	1,497	1,302
Intercompany charges, net	(34)	(17)	(82)	(47)
Other	1,231	1,234	3,635	3,559
OPERATING EXPENSES	8,956	8,979	26,992	26,331
OPERATING INCOME	837	530	2,496	1,853
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	90	80	291	323
Interest, net	6	4	15	14
Intercompany charges, net	(74)	(52)	(192)	(134)
Other, net	(4)	(9)	(5)	(14)
INCOME BEFORE INCOME TAXES	855	553	2,605	2,042
PROVISION FOR INCOME TAXES	248	165	836	648
NET INCOME	607	388	1,769	1,394
COMPREHENSIVE INCOME	596	388	1,733	1,401
Non Guarantor Subsidiaries Member
Condensed Financial Statements Captions [Line Items]
REVENUES	2,024	1,876	6,136	5,796
OPERATING EXPENSES:
Salaries and employee benefits	602	528	1,707	1,616
Purchased transportation	695	680	2,170	2,092
Rentals and landing fees	89	86	263	253
Depreciation and amortization	59	51	170	152
Fuel	20	25	69	73
Maintenance and repairs	37	31	107	94
Intercompany charges, net	82	69	273	210
Other	315	295	911	896
OPERATING EXPENSES	1,899	1,765	5,670	5,386
OPERATING INCOME	125	111	466	410
OTHER INCOME (EXPENSE):
Interest, net	2	3	4	5
Intercompany charges, net	6	6	16	17
Other, net	11	1	17	1
INCOME BEFORE INCOME TAXES	144	121	503	433
PROVISION FOR INCOME TAXES	81	51	179	137
NET INCOME	63	70	324	296
COMPREHENSIVE INCOME	(75)	44	64	235
Consolidation Eliminations Member
Condensed Financial Statements Captions [Line Items]
REVENUES	(101)	(84)	(285)	(252)
OPERATING EXPENSES:
Purchased transportation	(57)	(43)	(147)	(118)
Rentals and landing fees	(1)	(1)	(4)	(4)
Other	(43)	(40)	(134)	(130)
OPERATING EXPENSES	(101)	(84)	(285)	(252)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(670)	(458)	(2,093)	(1,690)
INCOME BEFORE INCOME TAXES	(670)	(458)	(2,093)	(1,690)
NET INCOME	(670)	(458)	(2,093)	(1,690)
COMPREHENSIVE INCOME	$ (670)	$ (458)	$ (2,093)	$ (1,690)