Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Fair value assets and liabilities measured on recurring basis
Contingent acquisition liability, total change		$ 11.8
Level 1
Fair value assets and liabilities measured on recurring basis
Cash equivalents		163.0	$ 132.1
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
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
Contingent acquisition obligations	[1]	160.2	148.4
Fair Value, Total [Member]
Fair value assets and liabilities measured on recurring basis
Cash equivalents		163.0	132.1
Contingent acquisition obligations	[1]	$ 160.2	$ 148.4

[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 increase in this balance of $11.8 from December 31, 2018 to March 31, 2019 is primarily due to valuation adjustments and accretion. The amounts payable within the next twelve months are classified in accrued liabilities; any amounts payable thereafter are classified in other non-current liabilities.