Earnings per Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 31, 2018
EPS numerator:
Income from continuing operations, net of income taxes	$ 42.9	$ 120.0	$ 176.2	$ 328.3
Less: Series A Convertible Preferred Stock dividends	0.0	0.0	0.0	102.5
Less: Net income attributable to noncontrolling interests	2.4	2.7	8.1	0.6
Income from continuing operations attributable to common stockholders, before allocation of earnings to participating securities	40.5	117.3	168.1	225.2
Less: Earnings allocated to participating securities	0.0	0.0	0.0	6.4
Income from continuing operations attributable to common stockholders, after allocation of earnings to participating securities (1)	40.5	117.3	168.1	218.8
Loss from discontinued operations, net of income taxes	(3.4)	(3.6)	(6.8)	(4.9)
Less: Loss from discontinued operations allocated to participating securities	0.0	0.0	0.0	(0.1)
Loss from discontinued operations attributable to common stockholders, after allocation of earnings to participating securities	(3.4)	(3.6)	(6.8)	(4.8)
Net income attributable to common stockholders, after allocation of earnings to participating securities (1)	$ 37.1	$ 113.7	$ 161.3	$ 214.0
EPS denominator:
Weighted average shares outstanding — basic	107.0	124.5	107.7	122.7
Impact of dilutive securities	1.1	1.5	1.6	1.9
Weighted average shares outstanding — diluted	108.1	126.0	109.3	124.6
Basic EPS attributable to common stockholders:
Income from continuing operations, per basic share	$ 0.38	$ 0.94	$ 1.56	$ 1.78
Loss from discontinued operation, per basic share	(0.03)	(0.03)	(0.06)	(0.04)
Basic income per share (in dollars per share)	0.35	0.91	1.50	1.74
Diluted EPS attributable to common stockholders:
Income from continuing operations, per diluted share	0.37	0.93	1.54	1.76
Loss from discontinued operations, per diluted share	(0.03)	(0.03)	(0.06)	(0.04)
Diluted income per share (in dollars per share)	$ 0.34	$ 0.90	$ 1.48	$ 1.72
Earnings Per Share Table Footnotes
Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted				$ 0.1
Weighted Average Number of Shares Outstanding, Diluted				4.2
Earnings per share textuals
Antidilutive shares excluded from EPS calculation	0.7	0.0	0.7	0.0
Convertible Preferred Stock
Earnings per share textuals
Preferred stock, shares issued					30.0
Common Stock | Common Stock
Earnings per share textuals
Common stock, shares converted from convertible preferred stock					59.3