Total Stock Based Compensation Expense (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Aug. 31, 2012	Aug. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Accelerated stock option expense	$ 4	$ 4

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

No definition available.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration