Acquisitions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Business Combinations
Number of Businesses Acquired	6		3
Business Acquisition, Goodwill Amount	$ 53.0		$ 5.0
Cash Acquired from Acquisition	(4.1)		(1.2)
Business Acquisition, Cash Paid	35.6	[1]	2.1	[1]
Acquisition-related payments	0.7
Acquisitions, including deferred payments, net of cash acquired	34.9		2.1
Current Year Acquisition
Business Combinations
Business Acquisition, Cost of Investment	39.0		2.4
Prior-Year Acquisition
Business Combinations
Business Acquisition, Cost of Investment	$ 0.7		$ 0.9
IAN
Business Combinations
Number of Businesses Acquired	6
CMG
Business Combinations
Number of Businesses Acquired			3

[1] Of the total cash paid, $0.7 for the three months ended March 31, 2013 is classified under the financing section of the unaudited Consolidated Statements of Cash Flows within other financing activities. 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, $34.9 and $2.1 for the three months ended March 31, 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.