Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 103.2	$ 72.7	$ 117.3	$ 74.9
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	103.2	72.7	117.3	74.9
Distributed Earnings	0.0	0.0	0.0	(0.1)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(0.1)	5.6	167.8	10.7
Net Income (Loss) Available to Common Stockholders, Basic	103.1	78.3	285.1	85.5
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted	103.2	72.7	117.3	74.9
Net Income (Loss) Available to Common Stockholders, Diluted	$ 103.1	$ 78.3	$ 285.1	$ 85.6
Earnings Per Share, Basic and Diluted [Abstract]
Numerator for diluted net income per common share:	13.5	16.1	14.0	16.2
Plus dilutive effect of stock awards	0.1	0.2	0.1	0.2
Denominator for net income per common share:	0.0	0.0	0.0	0.1
Basic	13.6	16.3	14.1	16.5
Earnings Per Share, Diluted [Abstract]
Diluted	$ 7.60	$ 4.86	$ 20.36	$ 5.27
Diluted	7.55	4.81	20.26	5.18
Income (Loss) from Continuing Operations, Per Basic Share	7.61	4.52	8.38	4.62
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0.34	11.98	0.65
Income (Loss) from Continuing Operations, Per Diluted Share	7.57	4.47	8.34	4.53
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	$ (0.02)	$ 0.34	$ 11.92	$ 0.65