Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Balance Sheet Parenthetical [Abstract]
Temporary Equity, Par or Stated Value Per Share	$ 0.01	$ 0.01
Series A convertible preferred stock, authorized (in shares)	3.0	3.0
Series A preferred shares, redemption amount	$ 859	$ 825
Series A preferred shares, liquidation preference	$ 859	$ 825
Series A convertible preferred stock, issued (in shares)	0.9	0.8
Series A convertible preferred stock, outstanding (in shares)	0.9	0.8
Stockholders' Equity:
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock shares authorized (in shares)	100.0	100.0
Preferred Stock shares issued (in shares)	0.0	0.0
Preferred Stock shares outstanding (in shares)	0.0	0.0
Common Stock par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock shares authorized (in shares)	500.0	500.0
Common Stock shares issued (in shares)	118.0	122.0
Common Stock shares outstanding (in shares)	118.0	122.0