PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 10
Interest cost	24	35
Expected return on plan assets	(49)	(59)
Amortization of actuarial loss	30	30
Amortization of prior service cost (credit)	1	1
Total net periodic benefit cost	17	17
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Amortization of actuarial loss	2	1
Amortization of prior service cost (credit)	(1)	0
Total net periodic benefit cost	$ 2	$ 2