Debt - Senior Notes and Contingent Convertible Senior Notes Purchased Narrative (Details) (USD $)	9 Months Ended						9 Months Ended									9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Nov. 07, 2012	Sep. 30, 2013 7.625% Senior Notes Due 2013	Sep. 30, 2013 6.625% Senior Notes Due 2019	Sep. 30, 2013 Senior Notes	Sep. 30, 2013 Senior Notes 2.5% Contingent Convertible Senior Notes due 2037	Dec. 31, 2012 Senior Notes 2.5% Contingent Convertible Senior Notes due 2037	Sep. 30, 2013 Senior Notes 2.75% Contingent Convertible Senior Notes Due 2035	Dec. 31, 2012 Senior Notes 2.75% Contingent Convertible Senior Notes Due 2035	Sep. 30, 2013 Senior Notes 2.25% Contingent Convertible Senior Notes Due 2038	Dec. 31, 2012 Senior Notes 2.25% Contingent Convertible Senior Notes Due 2038	Sep. 30, 2013 Senior Notes 3.25% Senior Notes due 2016	Dec. 31, 2012 Senior Notes 3.25% Senior Notes due 2016	Sep. 30, 2013 Senior Notes 6.775% Senior Notes Due 2019	Sep. 30, 2012 Senior Notes 6.775% Senior Notes Due 2019	Dec. 31, 2012 Senior Notes 6.775% Senior Notes Due 2019	Sep. 30, 2013 Senior Notes 7.625% Senior Notes Due 2013	Dec. 31, 2012 Senior Notes 7.625% Senior Notes Due 2013	Sep. 30, 2013 Senior Notes 6.625% Senior Notes Due 2019	Dec. 31, 2012 Senior Notes 6.625% Senior Notes Due 2019	Sep. 30, 2013 Senior Notes 5.375% Senior Notes due 2021 [Member]	Dec. 31, 2012 Senior Notes 5.375% Senior Notes due 2021 [Member]	Sep. 30, 2013 Senior Notes 5.75% Senior Notes due 2023 [Member]	Dec. 31, 2012 Senior Notes 5.75% Senior Notes due 2023 [Member]	Sep. 30, 2013 Senior Notes 6.875% Senior Notes Due 2018	Dec. 31, 2012 Senior Notes 6.875% Senior Notes Due 2018	Sep. 30, 2013 Minimum Senior Notes
Long-Term Debt Instrument [Line Items]
Debt Outstanding Principal Amount																													$ 50,000,000
Debt Instrument, Interest Rate, Stated Percentage					7.625%	6.625%		2.50%		2.75%		2.25%		3.25%		6.775%			7.625%		6.625%		5.375%		5.75%		6.875%
Debt Instrument, Interest Rate, Effective Percentage								8.00%		6.86%		8.00%
Proceeds from issuance of senior notes, net of discount and offering costs	2,274,000,000	1,263,000,000					2,274,000,000										1,263,000,000
Long-term Debt																	1,300,000,000
Unsecured Debt				2,000,000,000
Debt Instrument Principal Amount Redeemed Percent																					35.00%
Long-term Debt, Gross	12,736,000,000		12,620,000,000					1,168,000,000	1,168,000,000	396,000,000	396,000,000	347,000,000	347,000,000	500,000,000	0	0		1,300,000,000	0	464,000,000	650,000,000	650,000,000	700,000,000	0	1,100,000,000	0	97,000,000	474,000,000
Debt Instrument, Face Amount							2,300,000,000
Write off of Deferred Debt Issuance Cost							5,000,000									19,000,000
Write-off of Debt Discount							32,000,000									14,000,000
Repayments of Notes Payable																			247,000,000
Debt Instrument, Repurchase Amount							405,000,000												221,000,000
Debt Instrument, Repurchased Face Amount																			217,000,000								377,000,000
Gain (Loss) on Repurchase of Debt Instrument							$ 37,000,000									$ 33,000,000