Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Changes in goodwill
Gross goodwill, beginning balance	$ 343.5	$ 292.0
Accumulated impairment losses, beginning balance	(266.5)	(266.5)
Net goodwill, beginning balance	77.0	25.5
Goodwill acquired	202.4	51.5
Other purchase price adjustments	2.8
Gross goodwill, ending balance	548.7	343.5
Accumulated impairment losses, ending balance	(266.5)	(266.5)
Net goodwill, ending balance	282.2	77.0
Gross goodwill balance deductible for tax purposes	$ 154.0

Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

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The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes.

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The aggregate amount of goodwill acquired in the period and allocated to the reportable segment. The value is stated at fair value based on the purchase price allocation.

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Gross amount, as of the balance sheet date, of the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable), in excess of the fair value of net assets acquired in one or more business combination transactions.

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