Series A Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 17, 2017	Dec. 04, 2015
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)	900,000		900,000		800,000
Payments of Dividends	$ 0		$ 0
Deemed dividend on Series A convertible preferred stock related to redemption	0	$ 0	0	$ (58)
Deemed dividend on modification of Series A convertible preferred stock	0	0	0	(4)
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)							820,000
Aggregate purchase price of preferred shares							$ 820
Preferred Stock, par value (in dollars per share)							$ 1,000
Direct Issuance Expenses							$ 26
Dividend rate							5.50%
Dividends, Preferred Stock, Paid-in-kind	11	$ 11	34	$ 34
Accrued Dividends	$ 3		$ 3		$ 3
Conversion Price Per Share At Option Of Holder			$ 30
Conversion rate per preferred share			33.333
Secondary offering by the preferred shareholders						342,000
Redeemed Shares of Preferred stock						90,000
Preferred Stock, Redemption Price Per Share						$ 48.47
Financial instruments subject to redemption, settlement terms, maximum number of shares	28,600,000.0		28,600,000.0		27,500,000