Debt (Details 2) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended			12 Months Ended	1 Months Ended	12 Months Ended		37 Months Ended	12 Months Ended						1 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2011 1.625% Series A, 1.50% Series B and 1.50% Series C Convertible Senior Notes	Jan. 31, 2011 1.625% Series A Convertible Senior Notes due December 2037	Dec. 31, 2010 1.625% Series A Convertible Senior Notes due December 2037	Dec. 31, 2009 1.625% Series A Convertible Senior Notes due December 2037	Dec. 31, 2010 1.625% Series A Convertible Senior Notes due December 2037	Dec. 31, 2011 1.50% Series B Convertible Senior Notes due December 2037	Dec. 31, 2010 1.50% Series B Convertible Senior Notes due December 2037	Dec. 31, 2009 1.50% Series B Convertible Senior Notes due December 2037	Dec. 31, 2011 1.50% Series C Convertible Senior Notes due December 2037 Y	Dec. 31, 2010 1.50% Series C Convertible Senior Notes due December 2037	Dec. 31, 2009 1.50% Series C Convertible Senior Notes due December 2037	Jan. 31, 2012 Debt 1.50% Series B Convertible Senior Notes due December 2037
Carrying amounts of Convertible Senior Notes
Principal amount outstanding						$ 11		$ 11	$ 30	$ 1,680		$ 1,722	$ 1,722
Unamortized discount										(55)		(59)	(117)
Total debt	11,221		13,536			11		11	30	1,625		1,663	1,605
Carrying amount of equity component						1		1	4	210		276	276
Convertible debt instrument effective interest rate (as a percent)												5.28%
Remaining period over which discount will be amortized (in years)												1
Interest expense						58	85		78	98	100	84	98	100
Aggregate principal amount of debt repurchased							901	1,288	1,700				478
Aggregate cash payment made for debt repurchased					11		865	1,288	1,700				453		30
Gain (loss) on retirement of debt	33	29					28						21
Gain (loss) on retirement of debt per diluted share													$ 0.07
Adjustment to additional paid-in capital associated with equity components of repurchased notes							$ 22						$ 8
Shares per note of Convertible Senior Notes				1,000