STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Comprehensive income:
Net Income (Loss) Attributable to Parent	$ 127.1	$ 105.1	$ 241.5	$ 218.0
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	0.0	0.0	0.1	0.1
Other comprehensive income	0.0	0.0	0.1	0.1
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	127.1	105.1	241.6	218.1
Tax on reclassification of loss to net income	$ 0.0	$ 0.0	$ 0.0	$ 0.0