Business Combinations, Goodwill and Other Intangible Assets, Business Combinations Activity (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) acquisition	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Number of Businesses Acquired | acquisition	28
Business Acquisitions, net of cash acquired	$ 483.9	$ 391.6	$ 38.2
Business Combinations, Guaranteed Deferred Acquisition Obligation	62.7	23.1	21.5
Contingent Consideration Earn-Out, Fair Value	103.3	105.1	10.3
Goodwill, acquired during period	529.8	280.8
Finite-lived intangible assets acquired	104.5	200.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	15.6	19.8
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	387.6
Business Acquisition, Pro Forma Revenue	7,268.0	6,844.1
Business Acquisition, Pro Forma Net Income (Loss)	341.4	473.2
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	3.6	2.8
Deferred acquisition obligations paid	53.9	51.8
Payments for Repurchase of Redeemable Noncontrolling Interest	2.8
Goodwill Additions, net of adjustments	539.8	288.3
Business Acquisition, Goodwill, Expected Tax Deductible Amount	176.4	104.1
Cash Paid For New Acquisitions And Contingent Earn Out Consideration		373.0
Redeemable Noncontrolling Interest	0.0	$ 0.0	$ 14.2
Maximum amount of the potential earn-out payments	$ 435.0
Number of acquisitions subject to potential earn-out payments provisions | acquisition	52