Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		May 31, 2017	May 31, 2016	May 31, 2015
Allowance For Doubtful Accounts [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		$ 73	$ 86	$ 81
Charged To Expenses		136	121	145
Deductions	[1]	94	134	140
Valuation Allowances And Reserves Ending Balance		115	73	86
Allowance For Revenue Adjustments [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		105	99	83
Charged To Other Accounts	[2]	941	692	740
Deductions	[3]	909	686	724
Valuation Allowances And Reserves Ending Balance		137	105	99
Inventory Valuation Allowance [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		218	207	212
Charged To Expenses		26	26	23
Deductions		7	15	28
Valuation Allowances And Reserves Ending Balance		$ 237	$ 218	$ 207

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

[2] Principally charged against revenue.

[3] Service failures, rebills and other.