Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Level 1
Fair value assets and liabilities measured on recurring basis
Cash equivalents		$ 176.7	$ 440.8
Short-term marketable securities		3.2	3.0
Long-term investments		0.4	0.4
Fair Value of Total Assets, Recurring		$ 180.3	$ 444.2
Fair value of assets measured on a recurring basis percentage of total assets		1.50%	3.60%
Contingent acquisition obligations	[1]	$ 0.0	$ 0.0
Level 2
Fair value assets and liabilities measured on recurring basis
Cash equivalents		0.0	0.0
Short-term marketable securities		0.0	0.0
Long-term investments		0.0	0.0
Fair Value of Total Assets, Recurring		$ 0.0	$ 0.0
Fair value of assets measured on a recurring basis percentage of total assets		0.00%	0.00%
Contingent acquisition obligations	[1]	$ 0.0	$ 0.0
Level 3
Fair value assets and liabilities measured on recurring basis
Cash equivalents		0.0	0.0
Short-term marketable securities		0.0	0.0
Long-term investments		0.0	0.0
Fair Value of Total Assets, Recurring		$ 0.0	$ 0.0
Fair value of assets measured on a recurring basis percentage of total assets		0.00%	0.00%
Contingent acquisition obligations	[1]	$ 157.0	$ 205.4
Fair Value, Total [Member]
Fair value assets and liabilities measured on recurring basis
Cash equivalents		176.7	440.8
Short-term marketable securities		3.2	3.0
Long-term investments		0.4	0.4
Fair Value of Total Assets, Recurring		$ 180.3	$ 444.2
Fair value of assets measured on a recurring basis percentage of total assets		1.50%	3.60%
Contingent acquisition obligations	[1]	$ 157.0	$ 205.4

[1] Contingent acquisition obligations includes deferred acquisition payments and unconditional obligations to purchase additional noncontrolling equity shares of consolidated subsidiaries. Fair value measurement of the obligations is based upon actual and projected operating performance targets as specified in the related agreements. The decrease in this balance of $48.4 from December 31, 2016 to June 30, 2017 is primarily due to payments of $75.2, partially offset by acquisitions and exercised options of $16.3. The amounts payable within the next twelve months are classified in accrued liabilities; any amounts payable thereafter are classified in other non-current liabilities.