Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		May 31, 2016	May 31, 2015	May 31, 2014
Allowance For Doubtful Accounts [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		$ 86	$ 81	$ 94
Charged To Expenses		121	145	130
Deductions	[1]	134	140	143
Valuation Allowances And Reserves Ending Balance		73	86	81
Allowance For Revenue Adjustments [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		99	83	82
Charged To Other Accounts	[2]	692	740	626
Deductions	[3]	686	724	625
Valuation Allowances And Reserves Ending Balance		105	99	83
Inventory Valuation Allowance [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		207	212	205
Charged To Expenses		26	23	20
Deductions		15	28	13
Valuation Allowances And Reserves Ending Balance		$ 218	$ 207	$ 212

[1] (a) Uncollectible accounts written off, net of recoveries.

[2] (b) Principally charged against revenue.

[3] (c) Service failures, rebills and other.