Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Pension Benefits	Sep. 30, 2011 Pension Benefits	Sep. 30, 2012 Pension Benefits	Sep. 30, 2011 Pension Benefits	Dec. 31, 2012 Pension Benefits Forecast	Sep. 30, 2012 Postretirement Benefits Other than Pensions	Sep. 30, 2011 Postretirement Benefits Other than Pensions	Sep. 30, 2012 Postretirement Benefits Other than Pensions	Sep. 30, 2011 Postretirement Benefits Other than Pensions
Pension and other postretirement benefits
SERP benefit payments				$ 7.0
Service cost		1.1	1.0	3.4	3.0		0.5	0.4	1.4	1.3
Interest cost		3.5	3.6	10.6	10.9		0.5	0.5	1.5	1.7
Expected return on plan assets		(3.8)	(3.7)	(11.4)	(11.2)
Recognized net actuarial loss		1.0	0.4	3.1	1.2			0.1	0.2	0.2
Amortization of prior service cost		0.1	0.1	0.2	0.2			0.1	0.1	0.3
Curtailment loss									0.3
SERP settlement charge	3.5			3.5
Net periodic benefit cost		1.9	1.4	9.4	4.1		1.0	1.1	3.5	3.5
Contribution by the company				$ 15.5		$ 20.0