CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 23.7	$ 65.7	$ 143.0	$ 166.7
Other comprehensive income (loss):
Loss on cash flow hedge	0.0	0.0	(1.5)	0.0
Reclassification adjustment transferred to Net income from cash flow hedges	0.6	0.6	1.3	1.2
Pension and other postretirement benefit costs	0.4	1.1	0.7	1.7
Total Comprehensive Income	$ 24.7	$ 67.4	$ 143.5	$ 169.6