PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 8	$ 21	$ 18
Interest cost	25	34	49	69
Expected return on plan assets	(53)	(57)	(102)	(116)
Amortization of actuarial loss	27	31	57	61
Amortization of prior service cost (credit)	0	1	1	2
Total net periodic benefit cost	9	17	26	34
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2	2
Amortization of actuarial loss	0	0	2	1
Amortization of prior service cost (credit)	1	0	0	0
Total net periodic benefit cost	$ 2	$ 1	$ 4	$ 3