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Other Long-term Liabilities - Changes in Aggregate Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Beginning of period $ 66.3 $ 55.5  
Additions [1]   11.8  
Change in cash flow estimate (1.8) (5.1)  
Accretion expense 3.6 4.7 $ 3.7
Retirement of ARO 0.2 (0.6)  
End of period $ 68.3 $ 66.3 $ 55.5
[1] Amount reflects additions of ARO related to the commencement of operations of Grand Prix.