Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013		May 31, 2012		May 31, 2011
Allowance For Doubtful Accounts [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance	$ 94		$ 97		$ 93
Charged To Expenses	167		160		152
Deductions	167	[1]	163	[1]	148	[1]
Valuation Allowances And Reserves Ending Balance	94		94		97
Allowance For Revenue Adjustments [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance	84		85		73
Charged To Other Accounts	573	[2]	570	[2]	532	[2]
Deductions	575	[3]	571	[3]	520	[3]
Valuation Allowances And Reserves Ending Balance	82		84		85
Inventory Valuation Allowance [Member]
Movement In Valuation Allowances And Reserves Roll Forward
Valuation Allowances And Reserves Beginning Balance	184		169		170
Charged To Expenses	24		15		13
Deductions	3				14
Valuation Allowances And Reserves Ending Balance	$ 205		$ 184		$ 169

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

[2] (b) Principally charged against revenue.

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