STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Comprehensive income:
Net income	$ 54.1	$ 33.1
Derivative instruments:
Reclassification of losses to net income, net of tax of $0 and $0, respectively	0.0	0.1
Other comprehensive income	0.0	0.1
Comprehensive income	$ 54.1	$ 33.2