RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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			$ 1	1	$ 2
Interest cost on benefit obligation	132			131	381	406
Projected benefit obligation at period end—Significant Plans	12,696				12,696
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	12,075				12,075
Funded status of the Significant Plans	(621)				(621)
Net amount recognized at period end
Benefit asset	36				36
Benefit liability	(657)				(657)
Net amount recognized on the balance sheet—Significant Plans	(621)				(621)
Amounts recognized in AOCI at period end
Prior service benefit	0				0
Net actuarial (loss) gain	(6,313)				(6,313)
Net amount recognized in equity-pretax	(6,313)				(6,313)
Accumulated benefit obligation at period end—Significant Plans	12,689				12,689
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	12,841		14,012		14,012
Period activity		$ (595)	(576)
Benefits earned during the period	0
Interest cost on benefit obligation	132
Actuarial gain	(60)
Benefits paid, net of participants’ contributions and government subsidy	(217)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans		12,841
Change in plan assets
Plan assets at fair value at beginning of year	12,156		12,725		12,725
Period activity		(220)	(349)
Actual return on plan assets	123
Company contributions, net of reimbursements	13
Benefits paid, net of participants’ contributions and government subsidy	(217)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans		12,156
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	6			9	19	20
Projected benefit obligation at period end—Significant Plans	658				658
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	376				376
Funded status of the Significant Plans	(282)				(282)
Net amount recognized at period end
Benefit asset	0				0
Benefit liability	(282)				(282)
Net amount recognized on the balance sheet—Significant Plans	(282)				(282)
Amounts recognized in AOCI at period end
Prior service benefit	0				0
Net actuarial (loss) gain	77				77
Net amount recognized in equity-pretax	77				77
Accumulated benefit obligation at period end—Significant Plans	658				658
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
Period activity		0	(32)
Benefits earned during the period	0
Interest cost on benefit obligation	6
Actuarial gain	0
Benefits paid, net of participants’ contributions and government subsidy	(15)
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	237		262		262
Period activity		(4)	(21)
Actual return on plan assets	1
Company contributions, net of reimbursements	153
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		237
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	35			38	111	112
Interest cost on benefit obligation	73			76	220	221
Projected benefit obligation at period end—Significant Plans	5,254				5,254
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	5,604				5,604
Funded status of the Significant Plans	350				350
Net amount recognized at period end
Benefit asset	850				850
Benefit liability	(500)				(500)
Net amount recognized on the balance sheet—Significant Plans	350				350
Amounts recognized in AOCI at period end
Prior service benefit	25				25
Net actuarial (loss) gain	(807)				(807)
Net amount recognized in equity-pretax	(782)				(782)
Accumulated benefit obligation at period end—Significant Plans	4,980				4,980
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	5,253		5,446		5,446
Period activity		(344)	151
Benefits earned during the period	20
Interest cost on benefit obligation	60
Actuarial gain	(59)
Benefits paid, net of participants’ contributions and government subsidy	(68)
Foreign exchange impact and other	48
Projected benefit obligation at period end—Significant Plans		5,253
Change in plan assets
Plan assets at fair value at beginning of year	5,610		5,823		5,823
Period activity		(328)	115
Actual return on plan assets	7
Company contributions, net of reimbursements	15
Benefits paid, net of participants’ contributions and government subsidy	(68)
Foreign exchange impact and other	40
Plan assets at fair value at period end—Significant Plans		5,610
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	2			3	7	7
Interest cost on benefit obligation	26			$ 27	77	$ 76
Projected benefit obligation at period end—Significant Plans	949				949
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	1,154				1,154
Funded status of the Significant Plans	205				205
Net amount recognized at period end
Benefit asset	205				205
Benefit liability	0				0
Net amount recognized on the balance sheet—Significant Plans	205				205
Amounts recognized in AOCI at period end
Prior service benefit	80				80
Net actuarial (loss) gain	(284)				(284)
Net amount recognized in equity-pretax	(204)				(204)
Accumulated benefit obligation at period end—Significant Plans	949				949
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	951		927		927
Period activity		(65)	89
Benefits earned during the period	2
Interest cost on benefit obligation	23
Actuarial gain	(61)
Benefits paid, net of participants’ contributions and government subsidy	(14)
Foreign exchange impact and other	48
Projected benefit obligation at period end—Significant Plans		951
Change in plan assets
Plan assets at fair value at beginning of year	1,089		1,109		1,109
Period activity		(78)	$ 58
Actual return on plan assets	23
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(14)
Foreign exchange impact and other	56
Plan assets at fair value at period end—Significant Plans		$ 1,089
Qualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	36				36
Qualified plans | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	(282)				(282)
Qualified plans | Non-U.S. plans | Pension Plans
Change in plan assets
Funded status of the Significant Plans	350				350
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	205				205
Nonqualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(657)				(657)
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