Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Defined Contribution Plans
Defined contribution plan expense recognized	$ 2.9	$ 2.7	$ 6.5	$ 6.1
Expected amount of contribution to defined contribution plans in current fiscal year	12.2		12.2
Maximum percentage of employee compensation match by employer to employee stock ownership plan			4.00%
Maximum percentage of employee compensation match by employer to non union employee stock ownership plan			50.00%
Shares held by the ESOP plan	1.7		1.7		1.8
Defined Benefit Plans
Components of net periodic benefit cost
Service cost	1.3	1.2	2.6	2.3
Interest cost	2.0	2.5	3.9	5.0
Expected return on plan assets	(3.1)	(3.5)	(6.1)	(7.1)
Amortization of unrecognized loss	1.4	1.3	2.8	2.6
Net periodic benefit cost	1.6	1.5	3.2	2.8
Company's contribution to pension plan	0		0
Defined Benefit Plans | Minimum | Forecast
Components of net periodic benefit cost
Company's contribution to pension plan			0
Company's required contribution to pension plan			0
Defined Benefit Plans | Maximum | Forecast
Components of net periodic benefit cost
Company's contribution to pension plan			4.0
Post-retirement Welfare Plans
Components of net periodic benefit cost
Interest cost	0.1	0.1	0.1	0.2
Amortization of unrecognized loss			0.1
Net periodic benefit cost	0.1	0.1	0.2	0.2
Executive supplemental and director defined benefit pension plans | Forecast
Components of net periodic benefit cost
Company's contribution to pension plan			$ 1.1