PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Changes in Fair Value of Plan Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year (estimated)		$ 4,930	$ 5,514
Adjustment for final fair value of plan assets		16	44
Actual return on plan assets		449	123
Foreign currency translation		38	(73)
Employer contributions and benefit payments		30	345
Plan participants’ contributions		0	0
Plan transfers		1	1
Benefits paid (includes lump sum and annuity transfers)	$ (664)	(1,745)	(1,024)
Fair value of plan assets at end of year (estimated)	4,930	3,719	4,930
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year (estimated)		18	0
Adjustment for final fair value of plan assets		0	0
Actual return on plan assets		1	0
Foreign currency translation		0	0
Employer contributions and benefit payments		15	36
Plan participants’ contributions		2	4
Plan transfers		0	0
Benefits paid (includes lump sum and annuity transfers)		(17)	(22)
Fair value of plan assets at end of year (estimated)	$ 18	$ 19	$ 18