Consolidated Condensed Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 73.8	$ 58.0
Other comprehensive income, net of tax
Gain on cash flow hedges		0.2	0.3
Amortization of unrecognized benefit costs	[1]	0.5	0.6
Other comprehensive income, net of tax		0.7	0.9
Comprehensive income		$ 74.5	$ 58.9

[1] Related to postretirement and postemployment benefits. See Note 5 for additional information.