Revenue Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Accounts receivable, net of allowance of $66.6 and $68.5, respectively	$ 4,179.9	$ 5,177.7
Accounts receivable, billable to clients	2,155.3	2,347.2
Contract assets	54.4	62.3
Contract liabilities (deferred revenue)	760.0	$ 688.5
Revenue, Remaining Performance Obligation, Amount	$ 556.2