Fair Value Measurements - Recurring Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash equivalents - money market funds	$ 206.9	$ 173.5
Deferred compensation plan assets	54.9	48.8
Deferred purchase price receivable	66.9	140.1
Total	329.7	362.9
Liabilities
Deferred compensation plan liabilities	51.3	47.7
Earn-out liabilities	24.6	38.3
Total	175.8	111.9
Level 1
Assets
Cash equivalents - money market funds	206.9	173.5
Deferred compensation plan assets	54.9	48.8
Deferred purchase price receivable	0.0	0.0
Total	261.8	222.3
Liabilities
Deferred compensation plan liabilities	51.3	47.7
Earn-out liabilities	0.0	0.0
Total	51.3	47.7
Level 2
Assets
Cash equivalents - money market funds	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Deferred purchase price receivable	0.0	0.0
Total	1.0	0.5
Liabilities
Deferred compensation plan liabilities	0.0	0.0
Earn-out liabilities	0.0	0.0
Total	99.9	25.9
Level 3
Assets
Cash equivalents - money market funds	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Deferred purchase price receivable	66.9	140.1
Total	66.9	140.1
Liabilities
Deferred compensation plan liabilities	0.0	0.0
Earn-out liabilities	24.6	38.3
Total	24.6	38.3
Foreign currency forward contracts
Assets
Derivative asset	1.0	0.5
Liabilities
Derivative liability	2.2	0.8
Foreign currency forward contracts | Level 1
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Foreign currency forward contracts | Level 2
Assets
Derivative asset	1.0	0.5
Liabilities
Derivative liability	2.2	0.8
Foreign currency forward contracts | Level 3
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Interest rate swaps
Liabilities
Derivative liability	97.7	25.1
Interest rate swaps | Level 1
Liabilities
Derivative liability	0.0	0.0
Interest rate swaps | Level 2
Liabilities
Derivative liability	97.7	25.1
Interest rate swaps | Level 3
Liabilities
Derivative liability	$ 0.0	$ 0.0