PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 9	$ 32	$ 27
Interest cost	24	35	73	104
Expected return on plan assets	(51)	(59)	(153)	(175)
Amortization of actuarial loss	29	31	86	92
Amortization of prior service cost (credit)	1	1	2	3
Total net periodic benefit cost	14	17	40	51
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	1	2	3
Amortization of actuarial loss	2	1	4	2
Amortization of prior service cost (credit)	0	(1)	0	(1)
Total net periodic benefit cost	$ 2	$ 1	$ 6	$ 4