SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) $ in Millions  | 
 Dec. 31, 2020  
USD ($) 
 | 
|---|---|
| Fair Value | |
| Assets and Liabilities: | |
| Deferred Compensation Plan Assets (1) | $ 42.3 | 
| Deferred Compensation Plan Liability (1) | (42.3) | 
| Total assets and liabilities | 0.0 | 
| Quoted Prices in Active Markets for Identical Assets (Level 1) | |
| Assets and Liabilities: | |
| Deferred Compensation Plan Assets (1) | 42.3 | 
| Deferred Compensation Plan Liability (1) | 0.0 | 
| Total assets and liabilities | 42.3 | 
| Significant Other Observable Inputs (Level 2) | |
| Assets and Liabilities: | |
| Deferred Compensation Plan Assets (1) | 0.0 | 
| Deferred Compensation Plan Liability (1) | (42.3) | 
| Total assets and liabilities | (42.3) | 
| Significant Unobservable Inputs (Level 3) | |
| Assets and Liabilities: | |
| Deferred Compensation Plan Assets (1) | 0.0 | 
| Deferred Compensation Plan Liability (1) | 0.0 | 
| Total assets and liabilities | $ 0.0 | 
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- Definition Represents the deferred compensation plan assets, fair value disclosure as of reporting period. No definition available. 
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- Definition Represents the deferred compensation plan liabilities, fair value disclosure as of reporting period. No definition available. 
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- References No definition available. 
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- Definition Fair value of asset after deduction of liability. No definition available. 
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