Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Fair value assets and liabilities measured on recurring basis
Cash equivalents		$ 2,391.8	$ 1,382.4
Contingent acquisition obligations	[1]	33.5	95.5
Contingent acquisition obligation, total change		$ (62.0)
Discount rate floor contingent acquisition obligations		1.00%
Discount rate floor long-term debt		0.40%
Discount rate ceiling long-term debt		3.40%
Level 1
Fair value assets and liabilities measured on recurring basis
Cash equivalents		$ 2,391.8	1,382.4
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]	$ 33.5	$ 95.5

[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 $62.0 from December 31, 2020 to December 31, 2021 is primarily due to payments related to our deferred acquisitions from prior-year acquisitions and the effect of the deconsolidation of a previously consolidated entity, partially offset by the exercises of redeemable non-controlling interest and valuation adjustments in our consolidated subsidiaries. The amounts payable within the next twelve months are classified in accrued liabilities; any amounts payable thereafter are classified in other non-current liabilities.