Pension and Postretirement Benefit Costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit costs
Service cost for benefits earned	$ 0.6	$ 0.5
Interest cost on projected benefit obligation	10.6	11.7
Expected return on plan assets	(14.9)	(15.9)
Amortization of prior service cost	0.2	0.2
Amortization of actuarial loss	16.4	12.2
Net periodic pension costs	12.9	8.7
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit costs
Service cost for benefits earned	3.9	3.6
Interest cost on projected benefit obligation	10.5	13.7
Amortization of prior service cost	(0.4)	0.7
Amortization of actuarial loss	6.0	8.1
Net periodic pension costs	$ 20.0	$ 26.1