RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		$ 13,815		$ 13,815
Benefits earned during the period	$ 0		$ 0	0	$ 0
Interest cost on benefit obligation	95		101	177	207
Change in plan assets
Plan assets at fair value at beginning of year		13,309		13,309
Net amount recognized at period end
Benefit asset	802			802
Benefit liability	(680)			(680)
Net amount recognized on the balance sheet—Significant Plans	122			122
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	(6,611)			(6,611)
Net amount recognized in equity-pretax	(6,611)			(6,611)
Accumulated benefit obligation at period end—Significant Plans	13,071			13,071
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	12,807	13,790		13,790
Quarter activity		(983)
Benefits earned during the period	0
Interest cost on benefit obligation	95
Actuarial loss	429
Benefits paid, net of participants’ contributions and government subsidy	(259)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	13,072	12,807		13,072
Change in plan assets
Plan assets at fair value at beginning of year	12,874	13,309		13,309
Quarterly activity		(435)
Actual return on plan assets	566
Company contributions, net of reimbursements	13
Benefits paid, net of participants’ contributions and government subsidy	(259)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	13,194	12,874		13,194
Funded status of the Significant Plans	122			122
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		559		559
Benefits earned during the period	0		0	0	0
Interest cost on benefit obligation	3		5	6	10
Change in plan assets
Plan assets at fair value at beginning of year		331		331
Net amount recognized at period end
Benefit asset	0			0
Benefit liability	(188)			(188)
Net amount recognized on the balance sheet—Significant Plans	(188)			(188)
Amounts recognized in AOCI at period end
Prior service benefit	97			97
Net actuarial (loss) gain	85			85
Net amount recognized in equity-pretax	182			182
Accumulated benefit obligation at period end—Significant Plans	516			516
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	522	559		559
Quarter activity		(37)
Benefits earned during the period	0
Interest cost on benefit obligation	3
Actuarial loss	0
Benefits paid, net of participants’ contributions and government subsidy	(9)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	516	522		516
Change in plan assets
Plan assets at fair value at beginning of year	323	331		331
Quarterly activity		(8)
Actual return on plan assets	10
Company contributions, net of reimbursements	4
Benefits paid, net of participants’ contributions and government subsidy	(9)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	328	323		328
Funded status of the Significant Plans	(188)			(188)
Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		8,629		8,629
Benefits earned during the period	38		34	77	71
Interest cost on benefit obligation	70		61	132	125
Change in plan assets
Plan assets at fair value at beginning of year		7,831		7,831
Net amount recognized at period end
Benefit asset	789			789
Benefit liability	(596)			(596)
Net amount recognized on the balance sheet—Significant Plans	193			193
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	(976)			(976)
Net amount recognized in equity-pretax	(976)			(976)
Accumulated benefit obligation at period end—Significant Plans	5,641			5,641
Non-U.S. plans | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		2,248		2,248
Change in plan assets
Plan assets at fair value at beginning of year		1,500		1,500
Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	5,809	6,381		6,381
Quarter activity		(572)
Benefits earned during the period	22
Interest cost on benefit obligation	59
Actuarial loss	25
Benefits paid, net of participants’ contributions and government subsidy	(76)
Foreign exchange impact and other	108
Projected benefit obligation at period end—Significant Plans	5,947	5,809		5,947
Change in plan assets
Plan assets at fair value at beginning of year	5,927	6,331		6,331
Quarterly activity		(404)
Actual return on plan assets	157
Company contributions, net of reimbursements	18
Benefits paid, net of participants’ contributions and government subsidy	(76)
Foreign exchange impact and other	114
Plan assets at fair value at period end—Significant Plans	6,140	5,927		6,140
Funded status of the Significant Plans	193			193
Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		1,390		1,390
Benefits earned during the period	2		2	4	4
Interest cost on benefit obligation	24		$ 22	49	$ 46
Change in plan assets
Plan assets at fair value at beginning of year		1,146		1,146
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	54			54
Net actuarial (loss) gain	(243)			(243)
Net amount recognized in equity-pretax	(189)			(189)
Accumulated benefit obligation at period end—Significant Plans	1,020			1,020
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		277		277
Change in plan assets
Plan assets at fair value at beginning of year		8		8
Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	967	1,113		1,113
Quarter activity		(146)
Benefits earned during the period	1
Interest cost on benefit obligation	23
Actuarial loss	20
Benefits paid, net of participants’ contributions and government subsidy	(18)
Foreign exchange impact and other	27
Projected benefit obligation at period end—Significant Plans	1,020	967		1,020
Change in plan assets
Plan assets at fair value at beginning of year	1,094	1,138		1,138
Quarterly activity		(44)
Actual return on plan assets	24
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(18)
Foreign exchange impact and other	29
Plan assets at fair value at period end—Significant Plans	1,129	$ 1,094		1,129
Funded status of the Significant Plans	109			109
Qualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	802			802
Qualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(188)			(188)
Qualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	193			193
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	109			109
Nonqualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(680)			(680)
Nonqualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	0			0
Nonqualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	0			0
Nonqualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	$ 0			$ 0