Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		May. 31, 2015	May. 31, 2014	May. 31, 2013
Allowance For Doubtful Accounts [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		$ 81	$ 94	$ 94
Charged To Expenses		145	130	167
Deductions	[1]	140	143	167
Valuation Allowances And Reserves Ending Balance		86	81	94
Allowance For Revenue Adjustments [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		83	82	84
Charged To Other Accounts	[2]	740	626	573
Deductions	[3]	724	625	575
Valuation Allowances And Reserves Ending Balance		99	83	82
Inventory Valuation Allowance [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance		212	205	184
Charged To Expenses		23	20	24
Deductions		28	13	3
Valuation Allowances And Reserves Ending Balance		$ 207	$ 212	$ 205

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

[2] (b) Principally charged against revenue.

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