Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
(Loss) income from continuing operations, net of tax	$ (23.6)	$ 108.3	$ (46.2)	$ 120.2
Net loss attributable to noncontrolling interest	0.0	0.0	(0.1)	0.0
Net (loss) income from continuing operations, net of loss attributable to noncontrolling interests	(23.6)	108.3	(46.1)	120.2
Loss from discontinued operations, net of tax	(95.2)	(1.2)	(96.1)	(1.5)
Numerator for basic net (loss) income per common share	(118.8)	107.1	(142.2)	118.7
Numerator for basic net (loss) income per common share	(23.6)	108.3	(46.1)	120.2
Numerator for diluted net (loss) income from continuing operations per common share	$ (118.8)	$ 107.1	$ (142.2)	$ 118.7
Denominator for net (loss) income per common share:
Basic (in shares)	39.5	40.1	39.6	40.3
Plus dilutive effect of stock awards (in shares)	0.0	0.6	0.0	0.4
Diluted (in shares)	39.5	40.7	39.6	40.7
Net (loss) income per common share data, basic:
Continuing operations (in dollars per share)	$ (0.59)	$ 2.69	$ (1.16)	$ 2.99
Discontinued operations (in dollars per share)	(2.41)	(0.03)	(2.43)	(0.04)
Net (loss) income per common share data - basic (in dollars per share)	(3.00)	2.66	(3.59)	2.95
Net (loss) income per common share data, diluted:
Continuing operations (in dollars per share)	(0.59)	2.66	(1.16)	2.96
Discontinued operations (in dollars per share)	(2.41)	(0.03)	(2.43)	(0.04)
Net (loss) income per common share data - diluted (in dollars per share)	$ (3.00)	$ 2.63	$ (3.59)	$ 2.92
Anti-dilutive stock awards excluded from the calculation of diluted shares (in shares)	0.5	0.0	0.5	0.0