Condensed Consolidating Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Condensed Statement Of Income Captions [Line Items]
REVENUES	$ 17,010	$ 16,526	$ 51,886	$ 48,136
OPERATING EXPENSES:
Salaries and employee benefits	6,069	6,124	18,589	17,677
Purchased transportation	$ 4,253	$ 3,935	$ 12,566	$ 11,220
Type of cost, good or service [extensible list]	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember
Rentals and landing fees	$ 874	$ 873	$ 2,533	$ 2,526
Depreciation and amortization	851	786	2,487	2,293
Fuel	907	914	2,945	2,435
Maintenance and repairs	658	628	2,144	1,968
Business realignment costs	4	0	4	0
Other	2,483	2,408	7,468	7,073
OPERATING EXPENSES	16,099	15,668	48,736	45,192
OPERATING INCOME	911	858	3,150	2,944
OTHER INCOME (EXPENSE):
Interest, net	(135)	(125)	(393)	(363)
Other retirement plans income	158	143	474	436
Other, net	(3)	(2)	(22)	(22)
INCOME BEFORE INCOME TAXES	931	874	3,209	2,995
Provision for income taxes	192	(1,200)	700	(450)
NET INCOME	739	2,074	2,509	3,445
COMPREHENSIVE INCOME	819	2,151	2,350	3,503
Consolidation Eliminations [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUES	(100)	(136)	(302)	(353)
OPERATING EXPENSES:
Purchased transportation	$ (43)	$ (84)	$ (126)	$ (216)
Type of cost, good or service [extensible list]	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember
Rentals and landing fees	$ (1)	$ (2)	$ (4)	$ (6)
Maintenance and repairs	(2)		(2)
Other	(46)	(50)	(171)	(131)
OPERATING EXPENSES	(92)	(136)	(303)	(353)
OPERATING INCOME	(8)		1
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(755)	(2,076)	(2,654)	(3,484)
Other, net	8
INCOME BEFORE INCOME TAXES	(755)	(2,076)	(2,653)	(3,484)
NET INCOME	(755)	(2,076)	(2,653)	(3,484)
COMPREHENSIVE INCOME	(755)	(2,076)	(2,653)	(3,484)
Parent Company [Member] | Reportable Legal Entities [Member]
OPERATING EXPENSES:
Salaries and employee benefits	$ 28	$ 39	$ 110	$ 112
Type of cost, good or service [extensible list]	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember
Rentals and landing fees	$ 1	$ 2	$ 4	$ 4
Depreciation and amortization		1	1	1
Maintenance and repairs		1	1	1
Business realignment costs	4		4
Intercompany charges, net	(93)	(114)	(357)	(325)
Other	60	71	238	207
OPERATING EXPENSES			1
OPERATING INCOME			(1)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	739	2,074	2,509	3,445
Interest, net	(109)	(137)	(439)	(396)
Intercompany charges, net	149	140	454	403
Other, net	(40)	(3)	(14)	(7)
INCOME BEFORE INCOME TAXES	739	2,074	2,509	3,445
NET INCOME	739	2,074	2,509	3,445
COMPREHENSIVE INCOME	713	2,051	2,443	3,385
Guarantor Subsidiaries [Member[ | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUES	12,443	12,433	37,685	36,044
OPERATING EXPENSES:
Salaries and employee benefits	4,720	4,764	14,300	13,713
Purchased transportation	$ 2,749	$ 2,459	$ 7,780	$ 6,836
Type of cost, good or service [extensible list]	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember
Rentals and landing fees	$ 677	$ 684	$ 1,948	$ 1,951
Depreciation and amortization	731	670	2,133	1,958
Fuel	838	837	2,708	2,220
Maintenance and repairs	573	543	1,874	1,729
Intercompany charges, net	(397)	185	(772)	298
Other	1,771	1,596	4,991	4,664
OPERATING EXPENSES	11,662	11,738	34,962	33,369
OPERATING INCOME	781	695	2,723	2,675
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	16	2	145	39
Interest, net	(54)	11	44	35
Other retirement plans income	155	141	466	424
Intercompany charges, net	(89)	(78)	(335)	(220)
Other, net	71	104	18	88
INCOME BEFORE INCOME TAXES	880	875	3,061	3,041
Provision for income taxes	147	(1,197)	579	(573)
NET INCOME	733	2,072	2,482	3,614
COMPREHENSIVE INCOME	732	2,069	2,514	3,605
Non Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUES	4,667	4,229	14,503	12,445
OPERATING EXPENSES:
Salaries and employee benefits	1,321	1,321	4,179	3,852
Purchased transportation	$ 1,547	$ 1,560	$ 4,912	$ 4,600
Type of cost, good or service [extensible list]	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember	us-gaap:ShippingAndHandlingMember
Rentals and landing fees	$ 197	$ 189	$ 585	$ 577
Depreciation and amortization	120	115	353	334
Fuel	69	77	237	215
Maintenance and repairs	87	84	271	238
Intercompany charges, net	490	(71)	1,129	27
Other	698	791	2,410	2,333
OPERATING EXPENSES	4,529	4,066	14,076	12,176
OPERATING INCOME	138	163	427	269
OTHER INCOME (EXPENSE):
Interest, net	28	1	2	(2)
Other retirement plans income	3	2	8	12
Intercompany charges, net	(60)	(62)	(119)	(183)
Other, net	(42)	(103)	(26)	(103)
INCOME BEFORE INCOME TAXES	67	1	292	(7)
Provision for income taxes	45	(3)	121	123
NET INCOME	22	4	171	(130)
COMPREHENSIVE INCOME	$ 129	$ 107	$ 46	$ (3)