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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 |  |

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