Series A Convertible Preferred Stock (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 04, 2015
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)	900,000		800,000
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)				820,000
Aggregate purchase price of preferred shares				$ 820,000,000
Preferred stock, par value (in dollars per share)				$ 1,000
Direct issuance expenses				$ 26,000,000
Dividend rate				5.50%
Dividends, preferred stock, paid-in-kind	$ 12,000,000	$ 11,000,000
Accrued dividends	3,000,000		$ 3,000,000
Payments of Dividends	$ 0	$ 0
Conversion price per share at option of holder (in dollars per share)	$ 30.00
Conversion rate per preferred share (in shares)	33.333
Financial instruments subject to redemption, settlement terms, maximum number of shares (in shares)	29,400,000		29,000,000.0