STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Comprehensive income:
Net income	$ 58.8	$ 58.5	$ 112.9	$ 91.6
Derivative instruments:
Reclassification of losses to net income, net of tax of $0	0.1	0.0	0.1	0.0
Other comprehensive income	0.1	0.0	0.1	0.0
Comprehensive income	$ 58.9	$ 58.5	$ 113.0	$ 91.6