Subsequent Events (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended				1 Months Ended		1 Months Ended		2 Months Ended			1 Months Ended			2 Months Ended	6 Months Ended		1 Months Ended			2 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 03, 2013	Dec. 31, 2012	Jul. 31, 2013 5.25% Convertible Senior Notes due 2013 [Member]	Jun. 30, 2013 5.25% Convertible Senior Notes due 2013 [Member]	Jul. 31, 2013 4% Convertible Senior Notes due 2017 [Member]	Jun. 30, 2013 4% Convertible Senior Notes due 2017 [Member]	Jul. 31, 2013 4% Convertible Senior Notes due 2017 [Member]	Jul. 18, 2013 4% Convertible Senior Notes due 2017 [Member]	Jun. 03, 2013 4% Convertible Senior Notes due 2017 [Member]	Jul. 31, 2013 8% Convertible Perpetual Preferred Stock [Member]	Jun. 30, 2013 8% Convertible Perpetual Preferred Stock [Member]		Jul. 31, 2013 8% Convertible Perpetual Preferred Stock [Member]	Jun. 30, 2013 8% Convertible Perpetual Preferred Stock [Member]	Jul. 09, 2013 8% Convertible Perpetual Preferred Stock [Member]	Jul. 31, 2013 5.75% Convertible Perpetual Preferred Stock, Series 1 [Member]	Jun. 30, 2013 5.75% Convertible Perpetual Preferred Stock, Series 1 [Member]		Jul. 31, 2013 5.75% Convertible Perpetual Preferred Stock, Series 1 [Member]	Jun. 30, 2013 5.75% Convertible Perpetual Preferred Stock, Series 1 [Member]	Jul. 09, 2013 5.75% Convertible Perpetual Preferred Stock, Series 1 [Member]
Subsequent Event [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.30%		4.00%
Debt Conversion, Converted Instrument, Expiration or Due Date								Jul. 18, 2013
Preferred Stock, Dividend Rate, Percentage																8.00%						5.75%
Preferred Stock Conversion, Converted Instrument, Expiration or Due Date													Jul. 09, 2013						Jul. 09, 2013
Convertible Debt, Fair Value										$ 0	$ 237
Debt Conversion, Converted Instrument, Amount					1.0		26.0	211.0
Convertible Equity, Fair Value	782			0									30			30	1		229			229	0
Conversion of Stock, Amount Converted												0	29	[1]				29	200	[1]
Royalty Trust Units Issued, Conversion of Debt or Equity Instrument							1,800,000	14,500,000	16,300,000			0	2,000,000	[1]	2,000,000			2,000,000	13,700,000	[1]	15,700,000
Payments for Repurchase of Preferred Stock and Preference Stock	202	0
Royalty Trust Units, Fair Value Disclosure			$ 27								$ 25

[1] Conversions of preferred stock in June 2013 included cash consideration of $202 million and royalty trust units with a value of $27 million