Consolidated Condensed Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 11.1		$ 62.8		$ 119.6		$ 155.7
Other comprehensive income, net of tax
Net unrealized gains on cash flow hedges	0.1		0.8		0.4		1.1
Amortization of unrecognized benefit costs	0.2	[1]	0.6	[1]	1.6	[1]	2.0	[1]
Change in benefit obligation due to remeasurement	(0.7)		0		(0.7)		0
Increase in unrecognized postemployment costs	0		0		(8.2)		0
Recognized benefit costs due to settlement	0		1.6		0		1.6
Other comprehensive income (loss), net of tax	$ (0.4)		$ 3.0		$ (6.9)		$ 4.7

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