Acquisitions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Business Combinations
Number of Businesses Acquired	8		11
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	$ 67.0		$ 205.0
Business Acquisition, Cost of Investments	75.7		176.7
Cash Acquired from Acquisitions	(4.7)		(14.6)
Business Acquisition, Operating Expenses	1.6	[1]	3.2	[1]
Business Acquisitions, Total Cash Paid	77.3	[2]	179.9	[2]
Acquisition-related payments	27.5		36.1
Acquisitions, including deferred payments, net of cash acquired	(48.2)		(140.6)
Current-Year Acquisitions
Business Combinations
Business Acquisition, Cost of Investments	51.9		154.3
Prior-Year Acquisitions
Business Combinations
Business Acquisition, Cost of Investments	$ 28.5		$ 37.0
IAN
Business Combinations
Number of Businesses Acquired	7		7
CMG
Business Combinations
Number of Businesses Acquired	1		4

[1] Represents cash payments made that were either in excess of the contractual value or contingent upon the future employment of the former owners of acquired companies.

[2] Of the total cash paid, $27.5 and $36.1 for the nine months ended September 30, 2013, and 2012, respectively, are classified under the financing section of the unaudited Consolidated Statements of Cash Flows within acquisition-related payments. These amounts relate to increases in our ownership interests in our consolidated subsidiaries, as well as deferred payments for acquisitions that closed on or after January 1, 2009. Of the total cash paid, $48.2 and $140.6 for the nine months ended September 30, 2013, and 2012, respectively, are classified under the investing section of the unaudited Consolidated Statements of Cash Flows within acquisitions, including deferred payments, net of cash acquired. These amounts relate to initial payments for new transactions and deferred payments for acquisitions that closed prior to January 1, 2009.