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Debt - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Debt Instrument [Line Items]        
Cash payments paid for interest     $ 53.4 $ 58.6
Amortization of treasury lock settlements $ 1.3 $ 1.3 3.9 4.0
Amortization of financing costs 0.7 $ 0.7 2.1 $ 2.0
Senior Notes | Fixed-Rate Senior Notes        
Debt Instrument [Line Items]        
Book value of fixed rate debt 2,496.8   2,496.8  
Long-term debt (fixed-rate debt), fair value $ 2,607.0   $ 2,607.0