Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employee Benefit Plans
Curtailment charges recorded to write-off previously unrecognized prior service costs	$ 1.5
Expected annual effect of plan changes on future retirement plans expense	2.0
Change in projected benefit obligation
Balance at beginning of the year	112.6	96.1
Service cost	5.3	4.6	4.1
Administration cost	(0.6)	(1.0)
Interest cost	6.0	5.7	5.2
Actuarial loss	13.6	10.2
Benefits paid	(3.2)	(3.0)
Curtailment adjustment	(12.5)
Balance at end of year	121.2	112.6	96.1
Change in fair value of plan assets
Balance at beginning of the year	90.3	66.6
Actual gain on assets	14.1	7.4
Employer contributions	7.8	20.3
Administration cost	(0.6)	(1.0)
Benefits paid	(3.2)	(3.0)
Fair value of plan assets at end of the year	108.4	90.3	66.6
Funded status at end of year	(12.8)	(22.3)
Amounts recognized in the consolidated balance sheet
Current liabilities	(0.2)	(0.1)
Noncurrent liabilities	(12.6)	(22.2)
Net amount recognized	(12.8)	(22.3)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	31.1	39.3
Prior service cost		1.7
Net amount recognized	31.1	41.0
Information for pension plans with an accumulated benefit obligation in excess of plan assets
Projected benefit obligation	13.7	112.6
Accumulated benefit obligation	13.7	102.8
Fair value of plan assets		90.3
Information for pension plans with plan assets in excess of accumulated benefit obligation
Projected benefit obligation	107.6
Accumulated benefit obligation	107.6
Fair value of plan assets	108.4
Components of net periodic benefit cost
Service cost-benefits earned	5.3	4.6	4.1
Interest costs on benefits obligation	6.0	5.7	5.2
Expected return on assets	(7.5)	(6.0)	(4.0)
Prior service cost amortization	0.3	0.3	0.3
Net actuarial loss amortization	2.7	2.3	3.0
Curtailment charge	1.5
Net periodic benefit cost	8.3	6.9	8.6
Estimated amount that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year
Net actuarial loss	$ 0.6