RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		$ 12,655		$ 12,655
Benefits earned during the period	$ 0		$ 0	0	$ 1
Interest cost on benefit obligation	123		126	253	249
Projected benefit obligation at period end—Significant Plans	13,475			13,475
Change in plan assets
Plan assets at fair value at beginning of year		11,490		11,490
Plan assets at fair value at period end—Significant Plans	12,631			12,631
Funded status of the Significant Plans	(844)			(844)
Net amount recognized at period end
Benefit asset	0			0
Benefit liability	(844)			(844)
Net amount recognized on the balance sheet—Significant Plans	(844)			(844)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	(7,101)			(7,101)
Net amount recognized in equity-pretax	(7,101)			(7,101)
Accumulated benefit obligation at period end—Significant Plans	13,469			13,469
U.S. | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		25		25
Change in plan assets
Plan assets at fair value at beginning of year		0		0
U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	13,038	12,630		12,630
First quarter activity		408
Benefits earned during the period	0
Interest cost on benefit obligation	122
Actuarial loss	548
Benefits paid, net of participants’ contributions and government subsidy	(233)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans		13,038
Change in plan assets
Plan assets at fair value at beginning of year	11,977	11,490		11,490
First quarter activity		487
Actual return on plan assets	449
Company contributions, net of reimbursements	438
Benefits paid, net of participants’ contributions and government subsidy	(233)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans		11,977
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		662		662
Benefits earned during the period	0		0	0	0
Interest cost on benefit obligation	6		7	13	13
Projected benefit obligation at period end—Significant Plans	710			710
Change in plan assets
Plan assets at fair value at beginning of year		345		345
Plan assets at fair value at period end—Significant Plans	348			348
Funded status of the Significant Plans	(362)			(362)
Net amount recognized at period end
Benefit asset	0			0
Benefit liability	(362)			(362)
Net amount recognized on the balance sheet—Significant Plans	(362)			(362)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	13			13
Net amount recognized in equity-pretax	13			13
Accumulated benefit obligation at period end—Significant Plans	710			710
U.S. | Postretirement Benefit Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		0		0
Change in plan assets
Plan assets at fair value at beginning of year		0		0
U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	675	662		662
First quarter activity		13
Benefits earned during the period	0
Interest cost on benefit obligation	6
Actuarial loss	42
Benefits paid, net of participants’ contributions and government subsidy	(13)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans		675
Change in plan assets
Plan assets at fair value at beginning of year	347	345		345
First quarter activity		2
Actual return on plan assets	9
Company contributions, net of reimbursements	5
Benefits paid, net of participants’ contributions and government subsidy	(13)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans		347
Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		7,149		7,149
Benefits earned during the period	35		38	71	76
Interest cost on benefit obligation	73		72	148	147
Projected benefit obligation at period end—Significant Plans	5,757			5,757
Change in plan assets
Plan assets at fair value at beginning of year		6,699		6,699
Plan assets at fair value at period end—Significant Plans	6,099			6,099
Funded status of the Significant Plans	342			342
Net amount recognized at period end
Benefit asset	920			920
Benefit liability	(578)			(578)
Net amount recognized on the balance sheet—Significant Plans	342			342
Amounts recognized in AOCI at period end
Prior service benefit	14			14
Net actuarial (loss) gain	(995)			(995)
Net amount recognized in equity-pretax	(981)			(981)
Accumulated benefit obligation at period end—Significant Plans	5,467			5,467
Non-U.S. plans | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		1,862		1,862
Change in plan assets
Plan assets at fair value at beginning of year		1,248		1,248
Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	5,580	5,287		5,287
First quarter activity		293
Benefits earned during the period	21
Interest cost on benefit obligation	60
Actuarial loss	172
Benefits paid, net of participants’ contributions and government subsidy	(79)
Foreign exchange impact and other	3
Projected benefit obligation at period end—Significant Plans		5,580
Change in plan assets
Plan assets at fair value at beginning of year	5,708	5,451		5,451
First quarter activity		257
Actual return on plan assets	206
Company contributions, net of reimbursements	14
Benefits paid, net of participants’ contributions and government subsidy	(79)
Foreign exchange impact and other	250
Plan assets at fair value at period end—Significant Plans		5,708
Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		1,159		1,159
Benefits earned during the period	2		3	4	5
Interest cost on benefit obligation	26		$ 25	52	$ 51
Projected benefit obligation at period end—Significant Plans	975			975
Change in plan assets
Plan assets at fair value at beginning of year		1,036		1,036
Plan assets at fair value at period end—Significant Plans	1,084			1,084
Funded status of the Significant Plans	109			109
Net amount recognized at period end
Benefit asset	109			109
Benefit liability	0			0
Net amount recognized on the balance sheet—Significant Plans	109			109
Amounts recognized in AOCI at period end
Prior service benefit	72			72
Net actuarial (loss) gain	(320)			(320)
Net amount recognized in equity-pretax	(248)			(248)
Accumulated benefit obligation at period end—Significant Plans	975			975
Non-U.S. plans | Postretirement Benefit Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		307		307
Change in plan assets
Plan assets at fair value at beginning of year		9		9
Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	914	852		852
First quarter activity		62
Benefits earned during the period	1
Interest cost on benefit obligation	23
Actuarial loss	48
Benefits paid, net of participants’ contributions and government subsidy	(19)
Foreign exchange impact and other	8
Projected benefit obligation at period end—Significant Plans		914
Change in plan assets
Plan assets at fair value at beginning of year	1,059	1,027		1,027
First quarter activity		32
Actual return on plan assets	62
Company contributions, net of reimbursements	218
Benefits paid, net of participants’ contributions and government subsidy	(19)
Foreign exchange impact and other	(236)
Plan assets at fair value at period end—Significant Plans		$ 1,059
Qualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(151)			(151)
Qualified plans | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	(362)			(362)
Qualified plans | Non-U.S. plans | Pension Plans
Change in plan assets
Funded status of the Significant Plans	342			342
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	109			109
Nonqualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(693)			(693)
Nonqualified plans | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	0			0
Nonqualified plans | Non-U.S. plans | Pension Plans
Change in plan assets
Funded status of the Significant Plans	0			0
Nonqualified plans | Non-U.S. plans | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	$ 0			$ 0