Shareholders' Equity and Long-Term Incentive Compensation - Common Stock and Treasury Stock (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of common shares issued, treasury shares and shares outstanding
Balance at the beginning of the period (in shares)	41,940,089	41,416,000	40,858,000
Restricted stock shares and restricted stock units (in shares)	280,000	337,000	198,000
Retirement of treasury stock (in shares)		0
Other (in shares)	431,000	187,000	360,000
Balance at the end of the period (in shares)	42,650,599	41,940,089	41,416,000
Amount of retirement of treasury stock		$ 0.0
Common Stock
Authorized shares (in shares)	200,000,000
Par value (in dollars per share)	$ 0.01
Summary of common shares issued, treasury shares and shares outstanding
Balance at the beginning of the period (in shares)	50,755,000	100,526,000	100,064,000
Restricted stock shares and restricted stock units (in shares)	0	42,000	102,000
Retirement of treasury stock (in shares)		(50,000,000)
Other (in shares)	431,000	187,000	360,000
Balance at the end of the period (in shares)	51,186,000	50,755,000	100,526,000
Amount of retirement of treasury stock		$ 0.5
Common Stock In Treasury
Summary of common shares issued, treasury shares and shares outstanding
Balance at the beginning of the period (in shares)	(8,815,000)	(59,110,000)	(59,206,000)
Restricted stock shares and restricted stock units (in shares)	280,000	295,000	96,000
Retirement of treasury stock (in shares)		50,000,000
Other (in shares)	0	0	0
Balance at the end of the period (in shares)	(8,535,000)	(8,815,000)	(59,110,000)
Amount of retirement of treasury stock		$ (2,948.1)
Paid-In Capital
Summary of common shares issued, treasury shares and shares outstanding
Amount of retirement of treasury stock		1,285.4
Retained Earnings (Deficit)
Summary of common shares issued, treasury shares and shares outstanding
Amount of retirement of treasury stock		$ 1,662.2