Share-Based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based compensation expense	$ 32	[1]	$ 18	[1]	$ 72	[1]	$ 44	[1]
Unrecognized share-based compensation	$ 55				$ 55				$ 33

[1] Includes $(2) million and $9 million of (benefit) expense recognized in merger integration-related costs for the three and nine months ended September 30, 2013, respectively. Includes $0 and $7 million of expense recognized in merger integration-related costs for the three and nine months ended September 30, 2012, respectively.