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Long-Term Debt - Fair Value of Long-Term Debt (Details) - USD ($)
$ in Millions
Mar. 31, 2020
Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Carrying value $ 3,491.9 $ 3,337.9
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value $ 3,429.4 $ 3,447.5