Fair Value Measurements - Recurring Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets
Cash equivalents - money market funds	$ 433.0	$ 206.9
Deferred compensation plan assets	45.7	54.9
Deferred purchase price receivable	165.7	66.9
Total	647.5	329.7
Liabilities
Deferred compensation plan liabilities	44.3	51.3
Earn-out liabilities	15.7	24.6
Total	238.4	175.8
Level 1
Assets
Cash equivalents - money market funds	433.0	206.9
Deferred compensation plan assets	45.7	54.9
Deferred purchase price receivable	0.0	0.0
Total	478.7	261.8
Liabilities
Deferred compensation plan liabilities	44.3	51.3
Earn-out liabilities	0.0	0.0
Total	44.3	51.3
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	3.1	1.0
Liabilities
Deferred compensation plan liabilities	0.0	0.0
Earn-out liabilities	0.0	0.0
Total	178.4	99.9
Level 3
Assets
Cash equivalents - money market funds	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Deferred purchase price receivable	165.7	66.9
Total	165.7	66.9
Liabilities
Deferred compensation plan liabilities	0.0	0.0
Earn-out liabilities	15.7	24.6
Total	15.7	24.6
Foreign currency forward contracts
Assets
Foreign currency forward contracts	3.1	1.0
Liabilities
Derivative liability	2.1	2.2
Foreign currency forward contracts \| Level 1
Assets
Foreign currency forward contracts	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Foreign currency forward contracts \| Level 2
Assets
Foreign currency forward contracts	3.1	1.0
Liabilities
Derivative liability	2.1	2.2
Foreign currency forward contracts \| Level 3
Assets
Foreign currency forward contracts	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Interest rate swaps
Liabilities
Derivative liability	176.3	97.7
Interest rate swaps \| Level 1
Liabilities
Derivative liability	0.0	0.0
Interest rate swaps \| Level 2
Liabilities
Derivative liability	176.3	97.7
Interest rate swaps \| Level 3
Liabilities
Derivative liability	$ 0.0	$ 0.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of liability recognized arising from contingent consideration in a business combination.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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