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Summary of Significant Accounting Policies - Goodwill and Other Indefinite-Lived Intangible Assets (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
segment
item
Dec. 31, 2019
USD ($)
segment
item
Dec. 31, 2018
USD ($)
item
segment
Goodwill and Other Indefinite-Lived Intangible Assets      
Number of operating segments | segment 1 1 1
Number of reportable segments | item 1 1 1
Impairment of goodwill $ 0.0 $ 0.0 $ 0.0
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) $ 67.8   $ 16.5