PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8	$ 8	$ 18	$ 16
Interest cost	34	40	69	83
Expected return on plan assets	(57)	(54)	(116)	(116)
Amortization of actuarial loss	31	28	61	58
Amortization of prior service cost (credit)	1	1	2	2
Settlement charge	0	(6)	0	449
Total net periodic benefit cost	17	17	34	492
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2	3
Amortization of actuarial loss	0	2	1	4
Amortization of prior service cost (credit)	0	(2)	0	(3)
Total net periodic benefit cost	$ 1	$ 1	$ 3	$ 4