Debt - Senior Notes and Contingent Convertible Senior Notes Purchased Narrative (Details) (USD $) In Millions, unless otherwise specified																	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Senior Notes	Dec. 31, 2013 Senior Notes	Mar. 31, 2014 Minimum Senior Notes	Mar. 31, 2014 Minimum COO Senior Notes [Member]	Mar. 31, 2014 2.5% Contingent Convertible Senior Notes due 2037 Senior Notes	Dec. 31, 2013 2.5% Contingent Convertible Senior Notes due 2037 Senior Notes	Mar. 31, 2014 2.75% Contingent Convertible Senior Notes Due 2035 Senior Notes	Dec. 31, 2013 2.75% Contingent Convertible Senior Notes Due 2035 Senior Notes	Mar. 31, 2014 2.25% Contingent Convertible Senior Notes Due 2038 Senior Notes	Dec. 31, 2013 2.25% Contingent Convertible Senior Notes Due 2038 Senior Notes	Mar. 31, 2014 3.25% Senior Notes due 2016 Senior Notes	Dec. 31, 2013 3.25% Senior Notes due 2016 Senior Notes	Mar. 31, 2014 6.625% Senior Notes Due 2019 Senior Notes	Dec. 31, 2013 6.625% Senior Notes Due 2019 Senior Notes	Mar. 31, 2014 6.625% Senior Notes Due 2019 COO Senior Notes [Member]	Mar. 31, 2014 5.375% Senior Notes due 2021 Senior Notes	Dec. 31, 2013 5.375% Senior Notes due 2021 Senior Notes	Mar. 31, 2014 5.75% Senior Notes due 2023 Senior Notes	Dec. 31, 2013 5.75% Senior Notes due 2023 Senior Notes	Mar. 31, 2014 6.875% Senior Notes Due 2018	Mar. 31, 2014 6.875% Senior Notes Due 2018 Senior Notes	Dec. 31, 2013 6.875% Senior Notes Due 2018 Senior Notes
Long-Term Debt Instrument [Line Items]
Equity Method Investment, Ownership Percentage			100.00%
Debt Outstanding Principal Amount					$ 50
Debt Instrument, Interest Rate, Stated Percentage							2.50%		2.75%		2.25%		3.25%		6.625%			5.375%		5.75%		6.625%	6.875%
Debt Instrument, Interest Rate, Effective Percentage							8.00%		6.86%		8.00%
Long-term Debt, Gross	12,969	12,886				50	1,168	1,168	396	396	347	347	500	500	650	650		700	700	1,100	1,100		97	97
Debt Instrument, Unamortized Discount			$ 284	$ 303
Debt Instrument Principal Amount Redeemed Percent																	35.00%