PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 9	$ 8		$ 27	$ 24
Interest cost	35	39		104	122
Expected return on plan assets	(59)	(54)		(175)	(170)
Amortization of actuarial loss	31	27		92	85
Amortization of prior service cost (credit)	1	1		3	3
Settlement charge	0	0	$ (6)	0	449
Total net periodic benefit cost	17	21		51	513
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	2		3	5
Amortization of actuarial loss	1	1		2	5
Amortization of prior service cost (credit)	(1)	(1)		(1)	(4)
Total net periodic benefit cost	$ 1	$ 2		$ 4	$ 6