Fair Value of Pension Plan Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	$ 470.8	$ 407.4
Target Allocation Percentage of Assets, Equity Securities	25.00%
Target Allocation Percentage of Assets, Debt Securities	47.00%
Target Allocation Percentage of Assets, Other	28.00%
Target Allocation Percentage	1
Equity Securities	20.00%	26.00%
Debt Securities	47.00%	47.00%
Other Plan Assets	33.00%	27.00%
Actual Plan Asset Allocations	100.00%	100.00%
Balance at beginning of period	57.2	43.8
Actual return on plan assets:
Assets sold during the year	0.1	(0.6)
Assets still held at year end	(1.8)	6.7
Net purchases, sales and settlements	29.5	1.5
Transfers in/out of Level 3	0	5.8
Balance at end of period	85.0	57.2
Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	49.5	32.8
Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	336.3	317.4
Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	85.0	57.2
Investment Fund [Member]
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	369.3	362.5
Balance at beginning of period	53.9	38.6
Actual return on plan assets:
Assets sold during the year	0.1	(0.4)
Assets still held at year end	(0.6)	6.5
Net purchases, sales and settlements	(9.6)	3.0
Transfers in/out of Level 3	0	6.2
Balance at end of period	43.8	53.9
Investment Fund [Member] | Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	18.4	19.5
Investment Fund [Member] | Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	307.1	289.1
Investment Fund [Member] | Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	43.8	53.9
Insurance Contracts [Member]
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	24.8	25.1
Insurance Contracts [Member] | Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	0	0
Insurance Contracts [Member] | Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	24.8	25.1
Insurance Contracts [Member] | Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	0	0
Limited Partnership [Member]
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	41.1	3.2
Balance at beginning of period	3.2	4.7
Actual return on plan assets:
Assets sold during the year	0	(0.2)
Assets still held at year end	(1.2)	0.2
Net purchases, sales and settlements	39.1	(1.5)
Transfers in/out of Level 3	0	0
Balance at end of period	41.1	3.2
Limited Partnership [Member] | Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	0	0
Limited Partnership [Member] | Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	0	0
Limited Partnership [Member] | Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	41.1	3.2
Other Plan Assets [Member]
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	35.6	16.6
Balance at beginning of period	0.1	0.5
Actual return on plan assets:
Assets sold during the year	0	0
Assets still held at year end	0	0
Net purchases, sales and settlements	0	0
Transfers in/out of Level 3	0	(0.4)
Balance at end of period	0.1	0.1
Other Plan Assets [Member] | Fair Value, Inputs, Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	31.1	13.3
Other Plan Assets [Member] | Fair Value, Inputs, Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	4.4	3.2
Other Plan Assets [Member] | Fair Value, Inputs, Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Fair Value of Plan Assets	$ 0.1	$ 0.1