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Summary of Significant Accounting Policies Lease Term (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Oct. 31, 2020	Dec. 31, 2019
Leases
Accounts Receivable, Allowance for Credit Loss, Current	$ 4.7		$ 5.1
Contract with Customer, Liability	18.4		8.4
Goodwill	$ 1,618.4		$ 1,486.9
The Creative Circle
Leases
Goodwill		$ 358.0
The Creative Circle \| Trademarks
Leases
Indefinite-lived Intangible Assets (Excluding Goodwill)		$ 66.1
Minimum [Member]
Leases
Lessee, Operating Lease, Term of Contract	6 months
Property, Plant and Equipment, Estimated Useful Lives	three
Maximum [Member]
Leases
Lessee, Operating Lease, Term of Contract	11 years
Property, Plant and Equipment, Estimated Useful Lives	five years