Capital Structure (Preferred Stock - Details 3)	3 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 13, 2016 USD ($)	May 24, 2016 USD ($)	Dec. 23, 2014 USD ($)	Dec. 31, 2013 USD ($)	Aug. 11, 2005 shares
Capital Structure
Preferred Stock Instrument, Interest Rate, Stated Percentage		282.20%	282.20%				362.50%
Loss on Extinguishment of Preferred Stock				$ 42,000,000
Redeemable Preferred Stock, Fair Value							$ 291,000,000
Consent Fees Paid, Preferred Stock		$ 0	$ 0	5,000,000
Temporary Equity, Redemption Percentage					1.00	1.00
Temporary Equity, Liquidation Preference						$ 344,500,000
Payments for Repurchase of Redeemable Preferred Stock	$ (226,000,000)	(226,000,000)	0	0
Gain on Redemption of Redeemable Preferred Stock	$ 78,000,000	(78,000,000)	0	0
2.822% convertible perpetual preferred stock; $0.01 par value; 250,000 shares issued and outstanding at December 31, 2015		0	302,000,000	$ 291,000,000	$ 304,000,000			$ 249,000,000
Preferred Stock, Accretion of Redemption Discount		$ 2,000,000	$ 11,000,000
Convertible Preferred Stock [Member]
Capital Structure
Preferred Stock, Shares Issued | shares									250,000
Preferred Stock, Dividend Rate, Percentage				3.625%
Preferred Stock, Dividend Rate Amended, Percentage		2.822%	2.822%	2.822%