Revenue Contract Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accounts receivable, net of allowance of $68.5 and $98.3, respectively	$ 5,177.7	$ 4,646.4
Accounts receivable, billable to clients	2,347.2	1,820.7
Contract with Customer, Asset, after Allowance for Credit Loss	62.3	51.8
Contract liabilities	688.5	657.8
Revenue, remaining performance obligation, amount	605.1
Net revenue	$ 9,107.9	$ 8,064.5