Condensed Consolidating Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Condensed Statement Of Income Captions [Line Items]
REVENUE	$ 17,487	$ 17,010	$ 51,859	$ 51,886
OPERATING EXPENSES:
Salaries and employee benefits	6,382	6,069	18,704	18,589
Purchased transportation	4,558	4,253	12,914	12,566
Rentals and landing fees	964	874	2,808	2,533
Depreciation and amortization	908	851	2,688	2,487
Fuel	879	907	2,639	2,945
Maintenance and repairs	684	658	2,226	2,144
Asset impairment charges			66
Business realignment costs		4		4
Other	2,701	2,483	7,872	7,468
OPERATING EXPENSES	17,076	16,099	49,917	48,736
OPERATING INCOME	411	911	1,942	3,150
OTHER INCOME (EXPENSE):
Interest, net	(155)	(135)	(443)	(393)
Other retirement plans income	168	158	504	474
Other, net	(4)	(3)	(15)	(22)
INCOME BEFORE INCOME TAXES	420	931	1,988	3,209
Provision for income taxes (benefit)	105	192	368	700
NET INCOME	315	739	1,620	2,509
COMPREHENSIVE INCOME (LOSS)	294	819	1,547	2,350
Consolidation Eliminations [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUE	(96)	(100)	(275)	(302)
OPERATING EXPENSES:
Purchased transportation	(45)	(43)	(121)	(126)
Rentals and landing fees	(3)	(1)	(6)	(4)
Maintenance and repairs		(2)	(1)	(2)
Other	(48)	(46)	(147)	(171)
OPERATING EXPENSES	(96)	(92)	(275)	(303)
OPERATING INCOME		(8)		1
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	(337)	(755)	(1,686)	(2,654)
Interest, net			1
Intercompany charges, net			(1)
Other, net		8
INCOME BEFORE INCOME TAXES	(337)	(755)	(1,686)	(2,653)
NET INCOME	(337)	(755)	(1,686)	(2,653)
COMPREHENSIVE INCOME (LOSS)	(337)	(755)	(1,686)	(2,653)
Parent Company [Member] | Reportable Legal Entities [Member]
OPERATING EXPENSES:
Salaries and employee benefits	24	28	66	110
Rentals and landing fees	2	1	6	4
Depreciation and amortization			1	1
Maintenance and repairs				1
Business realignment costs		4		4
Intercompany charges, net	(93)	(93)	(249)	(357)
Other	67	60	176	238
OPERATING EXPENSES				1
OPERATING INCOME				(1)
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	315	739	1,620	2,509
Interest, net	(159)	(109)	(476)	(439)
Other retirement plans income			1
Intercompany charges, net	160	149	485	454
Other, net	(1)	(40)	(10)	(14)
INCOME BEFORE INCOME TAXES	315	739	1,620	2,509
NET INCOME	315	739	1,620	2,509
COMPREHENSIVE INCOME (LOSS)	298	713	1,569	2,443
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUE	12,925	12,443	37,474	37,685
OPERATING EXPENSES:
Salaries and employee benefits	4,934	4,720	14,441	14,300
Purchased transportation	3,211	2,749	8,619	7,780
Rentals and landing fees	749	677	2,175	1,948
Depreciation and amortization	789	731	2,335	2,133
Fuel	839	838	2,497	2,708
Maintenance and repairs	597	573	1,966	1,874
Asset impairment charges			66
Intercompany charges, net	(574)	(397)	(1,677)	(772)
Other	1,842	1,771	5,261	4,991
OPERATING EXPENSES	12,387	11,662	35,683	34,962
OPERATING INCOME	538	781	1,791	2,723
OTHER INCOME (EXPENSE):
Equity in earnings of subsidiaries	22	16	66	145
Interest, net	3	(54)	23	44
Other retirement plans income	163	155	488	466
Intercompany charges, net	(120)	(89)	(357)	(335)
Other, net	11	71	38	18
INCOME BEFORE INCOME TAXES	617	880	2,049	3,061
Provision for income taxes (benefit)	82	147	388	579
NET INCOME	535	733	1,661	2,482
COMPREHENSIVE INCOME (LOSS)	535	732	1,620	2,514
Non-guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
REVENUE	4,658	4,667	14,660	14,503
OPERATING EXPENSES:
Salaries and employee benefits	1,424	1,321	4,197	4,179
Purchased transportation	1,392	1,547	4,416	4,912
Rentals and landing fees	216	197	633	585
Depreciation and amortization	119	120	352	353
Fuel	40	69	142	237
Maintenance and repairs	87	87	261	271
Intercompany charges, net	667	490	1,926	1,129
Other	840	698	2,582	2,410
OPERATING EXPENSES	4,785	4,529	14,509	14,076
OPERATING INCOME	(127)	138	151	427
OTHER INCOME (EXPENSE):
Interest, net	1	28	9	2
Other retirement plans income	5	3	15	8
Intercompany charges, net	(40)	(60)	(127)	(119)
Other, net	(14)	(42)	(43)	(26)
INCOME BEFORE INCOME TAXES	(175)	67	5	292
Provision for income taxes (benefit)	23	45	(20)	121
NET INCOME	(198)	22	25	171
COMPREHENSIVE INCOME (LOSS)	$ (202)	$ 129	$ 44	$ 46