FAIR VALUE MEASUREMENTS - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	$ 279	$ 438
Short-term investments	261	664
Net derivative contracts	42	31
Contingent consideration from acquisition of Green Motion (Note 2)	(56)
Level 1
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	279	438
Short-term investments	261	664
Net derivative contracts	0	0
Contingent consideration from acquisition of Green Motion (Note 2)	0
Level 2
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	0	0
Short-term investments	0	0
Net derivative contracts	42	31
Contingent consideration from acquisition of Green Motion (Note 2)	0
Level 3
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	0	0
Short-term investments	0	0
Net derivative contracts	0	$ 0
Contingent consideration from acquisition of Green Motion (Note 2)	$ (56)