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Summary of Significant Accounting Policies - Narrative (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Entity Information [Line Items]      
Cash and cash equivalents related to payment processor transactions $ 24.5 $ 25.4  
Depreciation 73.4 86.5 $ 97.4
Capitalized internal-use software costs 9.9 13.4  
Amortization of contract costs 644.6 614.7 597.1
Advertising expense 329.6 260.0 231.1
Prepaid advertising $ 9.3 6.3  
Foreign Exchange Forward Contracts | Cash Flow Hedging | Designated as Hedging Instrument      
Entity Information [Line Items]      
Remaining maturity of derivatives 18 months    
TSR-based PSUs      
Entity Information [Line Items]      
Performance period 3 years    
Other Income (Expense), Net      
Entity Information [Line Items]      
Foreign currency (losses) $ (12.3) $ (7.1) $ (10.4)
Dividend Rate | TSR-based PSUs      
Entity Information [Line Items]      
Measurement input for share-based compensation awards 0    
Minimum | TSR-based PSUs      
Entity Information [Line Items]      
Percent of originally granted PSUs received as shares on the settlement date 0.00%    
Maximum | TSR-based PSUs      
Entity Information [Line Items]      
Percent of originally granted PSUs received as shares on the settlement date 200.00%