Components of Non-Cash Convertible Debt Related Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Non Cash Convertible Debt Related Expense [Line Items]
Total non-cash convertible debt related expense	$ 6	$ 5
3.25% Cash Convertible Senior Notes due 2014
Non Cash Convertible Debt Related Expense [Line Items]
Debt discount accretion	6	6
3.25% Cash Convertible Senior Notes due 2014 | Convertible Note Hedge
Non Cash Convertible Debt Related Expense [Line Items]
Fair value changes related to the derivative	(27)	9
3.25% Cash Convertible Senior Notes due 2014 | Cash Conversion Option
Non Cash Convertible Debt Related Expense [Line Items]
Fair value changes related to the derivative	27	(11)
1.00% Senior Convertible Debentures due 2027
Non Cash Convertible Debt Related Expense [Line Items]
Debt discount accretion		$ 1