Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)
shares in Millions, $ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Fair value of long-term debt $ 4,700.0   $ 4,800.0
Carrying value of long-term debt 4,400.0   $ 4,400.0
Carrying value of equity investment 106.0    
Unrealized gain on on equity investment 11.9    
Other Current Assets      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Restricted cash and cash equivalents 17.9    
Other Current Liabilities      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Restricted cash and cash equivalents $ 17.9    
Stock options      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Antidilutive stock options (in shares) 0.0 0.0