Common Stock and Stock-Based Compensation - Total Stock-Based Compensation Expense (Detail) - USD ($) $ in Millions		12 Months Ended
		May. 31, 2015	May. 31, 2014	May. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost		$ 19	$ 15	$ 22
Stock-based compensation expense		191	177	174
General and Administrative Expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		191	177	174
General and Administrative Expense | Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	[1]	136	125	123
General and Administrative Expense | Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		31	30	32
General and Administrative Expense | Employee Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		$ 24	$ 22	$ 19

[1] Expense for stock options includes the expense associated with stock appreciation rights. Accelerated stock option expense is recorded for employees eligible for accelerated stock option vesting upon retirement. Accelerated stock option expense for the years ended May 31, 2015, 2014 and 2013 was $19 million, $15 million and $22 million, respectively.