CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 37.9	$ 69.8	$ 177.3	$ 212.8
Other comprehensive income (loss):
Loss on cash flow hedge	0.0	0.0	0.0	(1.5)
Reclassification adjustment transferred to Net income from cash flow hedges	0.2	0.6	1.0	1.9
Pension and other postretirement benefit costs	(0.1)	0.1	1.4	0.8
Total Comprehensive Income	$ 38.0	$ 70.5	$ 179.7	$ 214.0