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FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Percentage of funds reported on a lag 86.00% 68.00%
Reported Value Measurement    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Senior notes $ 1,310 $ 1,808
Estimate of Fair Value    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Senior notes $ 1,485 $ 1,896