RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	87			87	264	294
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	865				865
Benefit liability	(668)				(668)
Net amount recognized on the balance sheet—Significant Plans	197				197
Amounts recognized in AOCI at period end
Prior service benefit	0				0
Net actuarial (loss) gain	(6,580)				(6,580)
Net amount recognized in equity-pretax	(6,580)				(6,580)
Accumulated benefit obligation at period end—Significant Plans	12,845				12,845
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	13,072		13,790		13,790
Quarter activity		$ 265	(983)
Benefits earned during the period	0
Interest cost on benefit obligation	87
Actuarial gain	(63)
Benefits paid, net of participants’ contributions and government subsidy	(249)
Settlement gain	0
Curtailment gain	0
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	12,847	13,072			12,847
Change in plan assets
Plan assets at fair value at beginning of year	13,194		13,309		13,309
Quarterly activity		320	(435)
Actual return on plan assets	86
Company contributions, net of reimbursements	13
Benefits paid, net of participants’ contributions and government subsidy	(249)
Settlement gain	0
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	13,044	13,194			13,044
Funded status of the Significant Plans	197				197
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			4	9	14
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	(176)				(176)
Net amount recognized on the balance sheet—Significant Plans	(176)				(176)
Amounts recognized in AOCI at period end
Prior service benefit	94				94
Net actuarial (loss) gain	86				86
Net amount recognized in equity-pretax	180				180
Accumulated benefit obligation at period end—Significant Plans	503				503
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	516		559		559
Quarter activity		(6)	(37)
Benefits earned during the period	0
Interest cost on benefit obligation	3
Actuarial gain	(4)
Benefits paid, net of participants’ contributions and government subsidy	(12)
Settlement gain	0
Curtailment gain	0
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	503	516			503
Change in plan assets
Plan assets at fair value at beginning of year	328		331		331
Quarterly activity		5	(8)
Actual return on plan assets	1
Company contributions, net of reimbursements	10
Benefits paid, net of participants’ contributions and government subsidy	(12)
Settlement gain	0
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	327	328			327
Funded status of the Significant Plans	(176)				(176)
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	36			38	113	109
Interest cost on benefit obligation	67			59	199	184
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	808				808
Benefit liability	(549)				(549)
Net amount recognized on the balance sheet—Significant Plans	259				259
Amounts recognized in AOCI at period end
Prior service benefit	(1)				(1)
Net actuarial (loss) gain	(884)				(884)
Net amount recognized in equity-pretax	(885)				(885)
Accumulated benefit obligation at period end—Significant Plans	5,425				5,425
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	5,947		6,381		6,381
Quarter activity		138	(572)
Benefits earned during the period	20
Interest cost on benefit obligation	58
Actuarial gain	(65)
Benefits paid, net of participants’ contributions and government subsidy	(87)
Settlement gain	(8)
Curtailment gain	(14)
Foreign exchange impact and other	(147)
Projected benefit obligation at period end—Significant Plans	5,704	5,947			5,704
Change in plan assets
Plan assets at fair value at beginning of year	6,140		6,331		6,331
Quarterly activity		213	(404)
Actual return on plan assets	32
Company contributions, net of reimbursements	16
Benefits paid, net of participants’ contributions and government subsidy	(87)
Settlement gain	(8)
Foreign exchange impact and other	(130)
Plan assets at fair value at period end—Significant Plans	5,963	6,140			5,963
Funded status of the Significant Plans	259				259
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	6	6
Interest cost on benefit obligation	25			$ 22	74	$ 68
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	128				128
Benefit liability	0				0
Net amount recognized on the balance sheet—Significant Plans	128				128
Amounts recognized in AOCI at period end
Prior service benefit	51				51
Net actuarial (loss) gain	(207)				(207)
Net amount recognized in equity-pretax	(156)				(156)
Accumulated benefit obligation at period end—Significant Plans	968				968
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	1,020		1,113		1,113
Quarter activity		53	(146)
Benefits earned during the period	1
Interest cost on benefit obligation	23
Actuarial gain	(29)
Benefits paid, net of participants’ contributions and government subsidy	(15)
Settlement gain	0
Curtailment gain	0
Foreign exchange impact and other	(32)
Projected benefit obligation at period end—Significant Plans	968	1,020			968
Change in plan assets
Plan assets at fair value at beginning of year	1,129		1,138		1,138
Quarterly activity		35	$ (44)
Actual return on plan assets	18
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(15)
Settlement gain	0
Foreign exchange impact and other	(36)
Plan assets at fair value at period end—Significant Plans	1,096	$ 1,129			1,096
Funded status of the Significant Plans	128				128
Qualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	865				865
Qualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(176)				(176)
Qualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	259				259
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	128				128
Nonqualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(668)				(668)
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