STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Comprehensive income:
Net income	$ 105.1	$ 81.5	$ 218.0	$ 173.1
Derivative instruments:
Amortization of losses included in net periodic benefit cost, net of tax of $0	0.0	0.1	0.1	0.1
Other comprehensive income	0.0	0.1	0.1	0.1
Comprehensive income	$ 105.1	$ 81.6	$ 218.1	$ 173.2