Corporate Debt (Details) shares in Millions	1 Months Ended	3 Months Ended			12 Months Ended
	Nov. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($)	Dec. 31, 2009 USD ($)
Debt Disclosure (Textuals) [Abstract]
Losses on early extinguishment of debt		$ 39,000,000	$ 73,000,000		$ 112,000,000	$ 71,000,000	$ 0
Debt Conversion, Original Debt, Amount								$ 1,700,000,000
Conversion of convertible debentures					$ 30,000,000	$ 5,000,000	$ 0
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares					2.9	0.5
Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value				$ 1,378,000,000	$ 1,008,000,000	$ 1,378,000,000
Unamortized discount				(12,000,000)	(11,000,000)	(12,000,000)
Total corporate debt				1,366,000,000	997,000,000	1,366,000,000
Corporate Debt By Maturity [Abstract]
2016					0
2017					0
2018					0
2019					8,000,000
2020					0
Thereafter					1,000,000,000
Face Value				1,378,000,000	1,008,000,000	1,378,000,000
Unamortized discount				(12,000,000)	(11,000,000)	(12,000,000)
Total corporate debt				1,366,000,000	997,000,000	1,366,000,000
Interest Bearing Total [Member] | Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value				1,340,000,000	1,000,000,000	1,340,000,000
Unamortized discount				(12,000,000)	(11,000,000)	(12,000,000)
Total corporate debt				1,328,000,000	989,000,000	1,328,000,000
Corporate Debt By Maturity [Abstract]
Face Value				1,340,000,000	1,000,000,000	1,340,000,000
Unamortized discount				(12,000,000)	(11,000,000)	(12,000,000)
Total corporate debt				1,328,000,000	$ 989,000,000	$ 1,328,000,000
Senior Notes Interest Bearing Five and Three Eighths Percent [Member]
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument maturity year					2022	2022
Senior Notes Interest Bearing Five and Three Eighths Percent [Member] | Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value	$ 540,000,000			540,000,000	$ 540,000,000	$ 540,000,000
Unamortized discount				(7,000,000)	(6,000,000)	(7,000,000)
Total corporate debt				$ 533,000,000	$ 534,000,000	$ 533,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage				5.375%	5.375%	5.375%
Corporate Debt By Maturity [Abstract]
Face Value	540,000,000			$ 540,000,000	$ 540,000,000	$ 540,000,000
Unamortized discount				(7,000,000)	(6,000,000)	(7,000,000)
Total corporate debt				533,000,000	$ 534,000,000	$ 533,000,000
Senior Notes Interest Bearing Four And Five Eighths Percent [Member]
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument maturity year					2023
Senior Notes Interest Bearing Four And Five Eighths Percent [Member] | Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value			460,000,000		$ 460,000,000
Unamortized discount					(5,000,000)
Total corporate debt					$ 455,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage					4.625%
Corporate Debt By Maturity [Abstract]
Face Value			460,000,000		$ 460,000,000
Unamortized discount					(5,000,000)
Total corporate debt					$ 455,000,000
Senior Notes Interest Bearing Six And Three Eighths Percent [Member]
Debt Disclosure (Textuals) [Abstract]
Repayments of Long-Term Debt and Associated Premiums, Interest and Fees			432,000,000
Losses on early extinguishment of debt			73,000,000
Debt Instrument, Redemption Premium			68,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument maturity year						2019
Senior Notes Interest Bearing Six And Three Eighths Percent [Member] | Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value				800,000,000		$ 800,000,000
Unamortized discount				(5,000,000)		(5,000,000)
Total corporate debt				$ 795,000,000		$ 795,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage				6.375%		6.375%
Corporate Debt By Maturity [Abstract]
Face Value				$ 800,000,000		$ 800,000,000
Unamortized discount				(5,000,000)		(5,000,000)
Total corporate debt				795,000,000		795,000,000
Senior Notes Interest Bearing Six And Three Fourths Percent and Six Percent [Member]
Debt Disclosure (Textuals) [Abstract]
Repayments of Long-Term Debt and Associated Premiums, Interest and Fees	460,000,000
Losses on early extinguishment of debt				$ 59,000,000		$ 59,000,000
Debt Instrument, Redemption Premium	$ 54,000,000
Senior Notes Interest Bearing Six And Three Fourths Percent [Member] | Corporate Debt Securities [Member]
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage				6.75%		6.75%
Senior Notes Interest Bearing Six Percent [Member] | Corporate Debt Securities [Member]
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage				6.00%		6.00%
Senior Notes Interest Bearing Eight Percent [Member] | Corporate Debt Securities [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Conversion, Converted Instrument, Amount								$ 400,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage								8.00%
Interest Bearing Twelve And Half Percent [Member] | Corporate Debt Securities [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Conversion, Converted Instrument, Amount								$ 1,300,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage								1.25%
Noninterest Bearing Convertible Debentures [Member]
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument maturity year					2019	2019
Noninterest Bearing Convertible Debentures [Member] | Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Face Value				$ 38,000,000	$ 8,000,000	$ 38,000,000
Unamortized discount				0	0	0
Total corporate debt				$ 38,000,000	$ 8,000,000	$ 38,000,000
Debt Instrument Interest Rate Stated Percentage [Abstract]
Debt instrument, interest rate, stated percentage				0.00%	0.00%	0.00%
Corporate Debt By Maturity [Abstract]
Face Value				$ 38,000,000	$ 8,000,000	$ 38,000,000
Unamortized discount				0	0	0
Total corporate debt				38,000,000	$ 8,000,000	38,000,000
Noninterest Bearing Convertible Debentures, Due 2019, Class A [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Instrument, Convertible, Conversion Ratio					10.34
Debt Instrument, Convertible, Conversion Ratio, Principal Amount					$ 1,000
Noninterest Bearing Convertible Debentures, Due 2019, Class A [Member] | Corporate Debt Securities [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Conversion, Original Debt, Amount								$ 1,700,000,000
Debt Conversion, Converted Instrument, Amount					$ 1,700,000,000
Debt Conversion, Converted Instrument, Shares Issued | shares					167.5
Noninterest Bearing Convertible Debentures, Due 2019, Class B [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Instrument, Convertible, Conversion Ratio					15.51
Debt Instrument, Convertible, Conversion Ratio, Principal Amount					$ 1,000
Noninterest Bearing Convertible Debentures, Due 2019, Class B [Member] | Corporate Debt Securities [Member]
Debt Disclosure (Textuals) [Abstract]
Debt Conversion, Original Debt, Amount								$ 2,000,000
Debt Conversion, Converted Instrument, Amount					$ 2,000,000
Debt Conversion, Converted Instrument, Shares Issued | shares					0.1
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 200,000,000	$ 250,000,000	$ 200,000,000
Line of Credit Facility, Increase (Decrease), Net			$ 50,000,000
Line of Credit Facility, Unrestricted Cash Minimum					100,000,000
Line of Credit Facility, Fair Value of Amount Outstanding					$ 0