Consolidated Condensed Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 5.3		$ 11.8	$ 79.1		$ 69.8
Other comprehensive income, net of tax
Gain on cash flow hedges		0.2		2.8	0.4		3.1
Amortization of unrecognized benefit costs and other	[1]	(0.2)		1.0	0.3		1.6
Recognized cost due to curtailment		0.1	[2]	0.0	0.1	[2]	0.0
Other comprehensive income, net of tax		0.1		3.8	0.8		4.7
Comprehensive income		$ 5.4		$ 15.6	$ 79.9		$ 74.5

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

[2] Related to the estimated curtailment loss for the SERP. See Note 5 for additional information.