FAIR VALUE - Put and Call Options Measured at Fair Value (Details) $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Put option
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of financial liability	$ 45	$ 28
Call option
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of financial asset	$ 503	$ 557
Options | Level 3 fair value measurement | Annualized volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.299	0.198
Options | Level 3 fair value measurement | Secured credit rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.004	0.022
Options | Level 3 fair value measurement | NOPAT
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.120	0.120
Options | Level 3 fair value measurement | Weighted average cost of capital
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.095	0.100
Options | Level 3 fair value measurement | Long term growth rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.030	0.030