Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		May 31, 2020	May 31, 2019	May 31, 2018
Allowance For Doubtful Accounts [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		$ 121	$ 199	$ 115
Charged To Expenses		442	295	246
Deductions	[1]	388	373	162
Valuation Allowances And Reserves Ending Balance		175	121	199
Allowance For Revenue Adjustments [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		179	202	137
Charged To Other Accounts	[2]	1,286	1,192	1,173
Deductions	[3]	1,250	1,215	1,108
Valuation Allowances And Reserves Ending Balance		215	179	202
Inventory Valuation Allowance [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		335	268	237
Charged To Expenses		33	28	27
Charged To Other Accounts			75	6
Deductions		33	36	2
Valuation Allowances And Reserves Ending Balance		$ 335	$ 335	$ 268

[1] Uncollectible accounts written off, net of recoveries, and other adjustments.

[2] Principally charged against revenue.

[3] Service failures, rebills and other.