Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 30.7	$ 44.9	$ 113.0	$ 130.8
Other Comprehensive Income (Loss) [Abstract]
Currency Translation Adjustments	0.0	0.1	0.0	(0.1)
Unrealized Gain (Loss) on Securities Net of Income Tax Expense of $–, $0.1, $– and $0.6	0.0	0.1	(0.1)	0.8
Defined Benefit Pension and Other Postretirement Benefit Plans Net of Income Tax Expense of $0.1, $0.1, $0.3 and $0.4	0.3	0.2	1.0	0.6
Total Other Comprehensive Income	0.3	0.4	0.9	1.3
Total Comprehensive Income	$ 31.0	$ 45.3	$ 113.9	$ 132.1