Earnings Per Share ("EPS") (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 9.1	$ 2.5
Payments of dividends	(51.1)	(50.2)
Net income available for common shareholders, basic and diluted	$ 8.4	$ 2.5
Weighted average shares for basic EPS	138,800,000	138,300,000
Dilutive potential shares from grants of RSUs, PRSUs and stock options	300,000	600,000
Weighted average shares for diluted EPS	139,100,000	138,900,000
Noncontrolling Interest
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Payments of dividends	$ (0.7)	$ 0.0
Noncontrolling Interest
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share, number of shares	2,000,000.0
Stock compensation plan
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share, number of shares	800,000	300,000