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Revenues from Contracts with Customers - Contract Costs (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Contract costs          
Contract cost asset $ 187.0   $ 187.0   $ 173.0
Practical expedient, incremental costs of obtaining a contract     true    
Impairment loss for contract cost asset     $ 0.0 $ 0.0  
Amortization expense of contract cost asset $ 9.0 $ 5.4 $ 16.1 $ 12.0