Pension and Other Postemployment Benefit (OPEB) Plans (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
Components of net periodic expense of Pension and OPEB plans
Non cash postretirement benefits curtailment gain	$ (45.0)	$ 0	$ (45.0)	$ 0
Pension Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	0.5	0.5	1.1	1.0
Interest cost	1.8	2.0	3.5	4.0
Expected return on plan assets	(2.0)	(2.1)	(4.1)	(4.2)
Amortization of net loss (gain)	0.7	0.3	1.4	0.6
Non cash postretirement benefits curtailment gain	0	0	0	0
Net periodic expense (benefit)	1.0	0.7	1.9	1.4
Other Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	0.1	0.2	0.1	0.4
Interest cost	0.2	0.2	0.3	0.4
Expected return on plan assets	(0.1)	0	(0.1)	0
Amortization of net loss (gain)	(3.3)	(2.4)	(5.7)	(4.8)
Non cash postretirement benefits curtailment gain	(45.0)	0	(45.0)	0
Net periodic expense (benefit)	$ (48.1)	$ (2.0)	$ (50.4)	$ (4.0)