Debt - Key Components of Convertible Debt (Detail) (Convertible Senior Notes 2011 and 2013, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Convertible Senior Notes 2011 and 2013
Debt Instrument [Line Items]
Contractual interest expense on the coupon	$ 27	$ 30	$ 58
Amortization of the discount component recognized as interest expense	58	61	116
Total interest expense on the convertible debt	$ 85	$ 91	$ 174