Debt - Senior Notes and Contingent Convertible Senior Notes Purchased Narrative (Details) (USD $)	6 Months Ended							6 Months Ended									6 Months Ended						6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Nov. 07, 2012	Jun. 30, 2013 6.775% Senior Notes Due 2019	Jun. 30, 2013 7.625% Senior Notes Due 2013	Jun. 30, 2013 6.625% Senior Notes Due 2019	Jun. 30, 2013 Senior Notes	Jun. 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	Jun. 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	Jun. 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	Jun. 30, 2013 Senior Notes 3.25% Senior Notes due 2016	Dec. 31, 2012 Senior Notes 3.25% Senior Notes due 2016	Jun. 30, 2013 Senior Notes 6.775% Senior Notes Due 2019	Jun. 30, 2012 Senior Notes 6.775% Senior Notes Due 2019	Dec. 31, 2012 Senior Notes 6.775% Senior Notes Due 2019	Jul. 15, 2013 Senior Notes 7.625% Senior Notes Due 2013	Jun. 30, 2013 Senior Notes 7.625% Senior Notes Due 2013	Dec. 31, 2012 Senior Notes 7.625% Senior Notes Due 2013	Jun. 30, 2013 Senior Notes 6.625% Senior Notes Due 2019	Dec. 31, 2012 Senior Notes 6.625% Senior Notes Due 2019	Jun. 30, 2013 Senior Notes 5.375% Senior Notes due 2021 [Member]	Dec. 31, 2012 Senior Notes 5.375% Senior Notes due 2021 [Member]	Jun. 30, 2013 Senior Notes 5.75% Senior Notes due 2023 [Member]	Dec. 31, 2012 Senior Notes 5.75% Senior Notes due 2023 [Member]	Jun. 30, 2013 Senior Notes 6.875% Senior Notes Due 2018	Dec. 31, 2012 Senior Notes 6.875% Senior Notes Due 2018	Jun. 30, 2013 Minimum	Jun. 30, 2013 Maximum Senior Notes COO Senior Notes [Member]
Long-Term Debt Instrument [Line Items]
Debt Outstanding Principal Amount																															$ 50,000,000
Debt Instrument Interest Rate Stated Percentage					6.775%	7.625%	6.625%		2.50%		2.75%		2.25%		3.25%		6.775%			7.625%	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	13,057,000,000		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		247,000,000	464,000,000	650,000,000	650,000,000	700,000,000	0	1,100,000,000	0	97,000,000	474,000,000		50,000,000
Debt Instrument, Face Amount								2,300,000,000												247,000,000
Write off of Deferred Debt Issuance Cost								5,000,000									19,000,000
Write-off of Debt Discount								32,000,000									14,000,000
Debt Instrument, Repurchase Amount								405,000,000													221,000,000
Debt Instrument, Repurchased Face Amount																	1,300,000,000				217,000,000								377,000,000
Gain (Loss) on Repurchase of Debt Instrument								$ 37,000,000									$ 33,000,000