Earnings Per Share and Common Stock (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
Earnings Per Share - Basic [Abstract]
Net Income	$ 34.2	$ 31.3	$ 104.7	$ 82.3
Average Common Shares	51.6	51.3	51.6	51.2
Earnings Per Share	$ 0.66	$ 0.61	$ 2.03	$ 1.61
Earnings Per Share - Diluted [Abstract]
Net Income	$ 34.2	$ 31.3	$ 104.7	$ 82.3
Average Common Shares	51.7	51.5	51.7	51.4
Earnings Per Share	$ 0.66	$ 0.61	$ 2.02	$ 1.60
Dilutive Securities (Shares)	0.1	0.2	0.1	0.2