Condensed Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income	$ 12.6	$ 17.9
Other comprehensive income, net of tax: Defined benefit pension and postretirement plans: [Abstract]
Amortization of prior service benefits included in net income, net of tax of ($1.2) and ($1.2)	(2.1)	(2.0)
Amortization of net loss included in net income, net of tax of $2.0 and $2.0	3.5	3.2
Other comprehensive income	1.4	1.2
Total comprehensive income	$ 14.0	$ 19.1