STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Comprehensive income:
Net Income (Loss) Attributable to Parent	$ 71.7	$ 58.8	$ 114.4	$ 112.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax	0.1	0.0	0.1	0.0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0.0	0.1	0.0	0.1
Other comprehensive income	0.1	0.1	0.1	0.1
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 71.8	$ 58.9	$ 114.5	$ 113.0