Pension and Other Postemployment Benefit (OPEB) Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Components of net periodic expense of Pension and OPEB plans
Curtailment (gain)			$ 0	$ (45.0)
Pension Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	0.6	0.5	1.7	1.7
Interest cost	1.7	1.8	5.1	5.5
Expected return on plan assets	(2.2)	(2.2)	(6.5)	(6.4)
Amortization of net loss (gain)	0.6	0.9	2.0	2.5
Amortization of prior service (credit)	0	0	(0.1)	(0.1)
Curtailment (gain)	0	0	0	0
Net periodic expense (benefit)	0.7	1.0	2.2	3.2
Other Benefits [Member]
Components of net periodic expense of Pension and OPEB plans
Service cost	0	0	0	0
Interest cost	0	0	0	0.1
Expected return on plan assets	0	0	0	0
Amortization of net loss (gain)	(3.2)	(3.1)	(9.6)	(6.1)
Amortization of prior service (credit)	(0.5)	(0.6)	(1.5)	(3.4)
Curtailment (gain)	0	0	0	(45.0)
Net periodic expense (benefit)	$ (3.7)	$ (3.7)	$ (11.1)	$ (54.4)