DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Fair Value Measurement Inputs (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Derivative [Line Items]
Expected timing until exercise of exchange option	4 years 11 months 12 days
Recurring
Derivative [Line Items]
Derivative liability	$ 239	$ 192
Preferred Units embedded derivative | Recurring
Derivative [Line Items]
Derivative liability	125	$ 139
Significant Unobservable Inputs (Level 3) | Preferred Units embedded derivative | Recurring
Derivative [Line Items]
Derivative liability	$ 125
Significant Unobservable Inputs (Level 3) | Measurement Input, Risk Free Interest Rate | Minimum
Derivative [Line Items]
Embedded derivative liability, measurement input	0.0562
Significant Unobservable Inputs (Level 3) | Measurement Input, Risk Free Interest Rate | Maximum
Derivative [Line Items]
Embedded derivative liability, measurement input	0.1150
Significant Unobservable Inputs (Level 3) | Measurement Input, Interest Rate Volatility
Derivative [Line Items]
Embedded derivative liability, measurement input	0.3833