Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Intangible Assets by Major Class [Line Items]
Finite Lived Intangible Asset Useful Life	3 years 10 months 24 days
Intangible asset amortization	$ 199	$ 157	$ 181