Pension and Other Post-Retirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Components of pension and other post retirement benefit costs
Service cost	$ 1.5	$ 1.2	$ 3.0	$ 2.7
Interest cost	5.0	5.2	9.9	10.4
Expected return on plan assets	(7.4)	(8.3)	(14.8)	(16.6)
Unrecognized prior service credit	(0.2)	(0.2)	(0.5)	(0.5)
Unrecognized net actuarial loss (gains)	2.5	1.6	5.0	3.6
Net costs (a)	1.4	(0.5)	2.6	(0.4)
Retiree Health and Life [Member]
Components of pension and other post retirement benefit costs
Service cost		0.1	0.1	0.1
Interest cost	0.5	0.6	1.0	1.1
Unrecognized prior service credit	(0.1)	(0.1)	(0.1)	(0.1)
Unrecognized net actuarial loss (gains)	(0.1)	(0.1)	(0.1)	(0.1)
Net costs (a)	$ 0.3	$ 0.5	$ 0.9	$ 1.0