Pension and Other Postretirement Benefit Plans (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of net periodic expense of Pension and OPEB plans
Non-cash postretirement benefits curtailment and settlement gain	$ 45.0	$ 0	$ 7.0
Pension Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	2.4	2.2
Interest cost	7.2	8.3
Expected return on plan assets	(8.4)	(8.0)
Amortization of net loss (gain)	3.0	1.5
Amortization of unrecognized prior service costs	(0.2)	(0.3)
Non-cash postretirement benefits curtailment and settlement gain	0	0
Net periodic expense (benefit)	4.0	3.7
Other Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	0	0.1
Interest cost	0.1	0.4
Expected return on plan assets	0	0
Amortization of net loss (gain)	(9.2)	(2.3)
Amortization of unrecognized prior service costs	(3.9)	(7.2)
Non-cash postretirement benefits curtailment and settlement gain	45.0	0
Net periodic expense (benefit)	$ (58.0)	$ (9.0)