RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		$ 14,040		$ 14,040
Benefits earned during the period	$ 0		$ 0	1	$ 1
Interest cost on benefit obligation	126		136	249	275
Projected benefit obligation at period end—Significant Plans	12,841			12,841
Change in plan assets
Plan assets at fair value at beginning of year		12,725		12,725
Plan assets at fair value at period end—Significant Plans	12,156			12,156
Funded status of the Significant Plans	(685)			(685)
Net amount recognized at period end
Benefit asset	0			0
Benefit liability	(685)			(685)
Net amount recognized on the balance sheet—Significant Plans	(685)			(685)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	(6,324)			(6,324)
Net amount recognized in equity-pretax	(6,324)			(6,324)
Accumulated benefit obligation at period end—Significant Plans	12,833			12,833
U.S. | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		28		28
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	13,436	14,012		14,012
First quarter activity		(576)
Benefits earned during the period	0
Interest cost on benefit obligation	126
Actuarial (gain) loss	(516)
Benefits paid, net of participants’ contributions and government subsidy	(206)
Curtailment loss	1
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans		13,436
Change in plan assets
Plan assets at fair value at beginning of year	12,376	12,725		12,725
First quarter activity		(349)
Actual return on plan assets				(27)
Company contributions, net of reimbursements				13
Benefits paid, net of participants’ contributions and government subsidy				(206)
Foreign exchange impact and other				0
Plan assets at fair value at period end—Significant Plans		12,376
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		699		699
Benefits earned during the period	0		0	0	0
Interest cost on benefit obligation	7		8	13	14
Projected benefit obligation at period end—Significant Plans	667			667
Change in plan assets
Plan assets at fair value at beginning of year		262		262
Plan assets at fair value at period end—Significant Plans	237			237
Funded status of the Significant Plans	(430)			(430)
Net amount recognized at period end
Benefit asset	0			0
Benefit liability	(430)			(430)
Net amount recognized on the balance sheet—Significant Plans	(430)			(430)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	79			79
Net amount recognized in equity-pretax	79			79
Accumulated benefit obligation at period end—Significant Plans	667			667
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	667	699		699
First quarter activity		(32)
Benefits earned during the period	0
Interest cost on benefit obligation	7
Actuarial (gain) loss	8
Benefits paid, net of participants’ contributions and government subsidy	(15)
Curtailment loss	0
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans		667
Change in plan assets
Plan assets at fair value at beginning of year	241	262		262
First quarter activity		(21)
Actual return on plan assets				0
Company contributions, net of reimbursements				11
Benefits paid, net of participants’ contributions and government subsidy				(15)
Foreign exchange impact and other				0
Plan assets at fair value at period end—Significant Plans		241
Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		7,433		7,433
Benefits earned during the period	38		38	76	74
Interest cost on benefit obligation	72		74	147	145
Projected benefit obligation at period end—Significant Plans	5,253			5,253
Change in plan assets
Plan assets at fair value at beginning of year		7,128		7,128
Plan assets at fair value at period end—Significant Plans	5,610			5,610
Funded status of the Significant Plans	357			357
Net amount recognized at period end
Benefit asset	847			847
Benefit liability	(490)			(490)
Net amount recognized on the balance sheet—Significant Plans	357			357
Amounts recognized in AOCI at period end
Prior service benefit	25			25
Net actuarial (loss) gain	(801)			(801)
Net amount recognized in equity-pretax	(776)			(776)
Accumulated benefit obligation at period end—Significant Plans	4,992			4,992
Non-U.S. plans | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year		1,987		1,987
Change in plan assets
Plan assets at fair value at beginning of year		1,305		1,305
Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	5,597	5,446		5,446
First quarter activity		151
Benefits earned during the period	22
Interest cost on benefit obligation	60
Actuarial (gain) loss	(96)
Benefits paid, net of participants’ contributions and government subsidy	(74)
Curtailment loss	0
Foreign exchange impact and other	(256)
Projected benefit obligation at period end—Significant Plans		5,597
Change in plan assets
Plan assets at fair value at beginning of year	5,938	5,823		5,823
First quarter activity		115
Actual return on plan assets				(22)
Company contributions, net of reimbursements				21
Benefits paid, net of participants’ contributions and government subsidy				(74)
Foreign exchange impact and other				(253)
Plan assets at fair value at period end—Significant Plans		5,938
Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year		1,261		1,261
Benefits earned during the period	3		2	5	4
Interest cost on benefit obligation	25		$ 25	51	$ 49
Projected benefit obligation at period end—Significant Plans	951			951
Change in plan assets
Plan assets at fair value at beginning of year		1,119		1,119
Plan assets at fair value at period end—Significant Plans	1,089			1,089
Funded status of the Significant Plans	138			138
Net amount recognized at period end
Benefit asset	(380)			(380)
Benefit liability	518			518
Net amount recognized on the balance sheet—Significant Plans	138			138
Amounts recognized in AOCI at period end
Prior service benefit	78			78
Net actuarial (loss) gain	(334)			(334)
Net amount recognized in equity-pretax	(256)			(256)
Accumulated benefit obligation at period end—Significant Plans	951			951
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		334		334
Change in plan assets
Plan assets at fair value at beginning of year		10		10
Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	1,016	927		927
First quarter activity		89
Benefits earned during the period	2
Interest cost on benefit obligation	22
Actuarial (gain) loss	(1)
Benefits paid, net of participants’ contributions and government subsidy	(15)
Curtailment loss	0
Foreign exchange impact and other	(73)
Projected benefit obligation at period end—Significant Plans		1,016
Change in plan assets
Plan assets at fair value at beginning of year	1,167	1,109		1,109
First quarter activity		58
Actual return on plan assets				20
Company contributions, net of reimbursements				0
Benefits paid, net of participants’ contributions and government subsidy				(15)
Foreign exchange impact and other				(83)
Plan assets at fair value at period end—Significant Plans		$ 1,167
Qualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(18)			(18)
Qualified plans | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	(430)			(430)
Qualified plans | Non-U.S. plans | Pension Plans
Change in plan assets
Funded status of the Significant Plans	357			357
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	138			138
Nonqualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(667)			(667)
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