Share-Based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based compensation expense	$ 27	[1]	$ 15	[1]
Unrecognized share-based compensation expense	$ 58				$ 33

[1] Includes $8 million and $4 million of expense recognized in Merger integration-related costs for the three months ended March 31, 2013 and 2012, respectively.