RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			$ 14,000		$ 14,000
Projected benefit obligation at September 30, 2017—Significant Plans	$ 13,926				13,926
Change in plan assets
Plan assets at fair value at beginning of year			12,363		12,363
Plan assets at fair value at September 30, 2017—Significant Plans	12,621				12,621
Funded status of the Significant Plans	(1,305)				(1,305)
Net amount recognized
Benefit asset	0				0
Benefit liability	(1,305)				(1,305)
Net amount recognized on the balance sheet—Significant Plans	(1,305)				(1,305)
Amounts recognized in AOCI
Prior service benefit	0				0
Net actuarial (loss) gain	(6,779)				(6,779)
Net amount recognized in equity-pretax	(6,779)				(6,779)
Accumulated benefit obligation at September 30, 2017—Significant Plans	13,920				13,920
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	14,158		13,972		13,972
Quarter activity		$ 161	25
Benefits earned during the period	1
Interest cost on benefit obligation	131
Actuarial loss	95
Benefits paid, net of participants’ contributions	(191)
Curtailment loss (gain)	1
Foreign exchange impact and other	(269)
Projected benefit obligation at September 30, 2017—Significant Plans		14,158
Change in plan assets
Plan assets at fair value at beginning of year	12,708		12,363		12,363
Quarter activity		186	159
Actual return on plan assets	310
Company contributions, net of reimbursements	63
Plan participants’ contributions	0
Benefits paid, net of government subsidy	(191)
Foreign exchange impact and other	(269)
Plan assets at fair value at September 30, 2017—Significant Plans		12,708
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			686		686
Projected benefit obligation at September 30, 2017—Significant Plans	736				736
Change in plan assets
Plan assets at fair value at beginning of year			129		129
Plan assets at fair value at September 30, 2017—Significant Plans	125				125
Funded status of the Significant Plans	(611)				(611)
Net amount recognized
Benefit asset	0				0
Benefit liability	(611)				(611)
Net amount recognized on the balance sheet—Significant Plans	(611)				(611)
Amounts recognized in AOCI
Prior service benefit	0				0
Net actuarial (loss) gain	39				39
Net amount recognized in equity-pretax	39				39
Accumulated benefit obligation at September 30, 2017—Significant Plans	736				736
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	742		686		686
Quarter activity		63	(7)
Benefits earned during the period	0
Interest cost on benefit obligation	6
Actuarial loss	2
Benefits paid, net of participants’ contributions	(14)
Curtailment loss (gain)	0
Foreign exchange impact and other	0
Projected benefit obligation at September 30, 2017—Significant Plans		742
Change in plan assets
Plan assets at fair value at beginning of year	126		129		129
Quarter activity		(3)	0
Actual return on plan assets	3
Company contributions, net of reimbursements	10
Plan participants’ contributions	0
Benefits paid, net of government subsidy	(14)
Foreign exchange impact and other	0
Plan assets at fair value at September 30, 2017—Significant Plans		126
Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			6,522		6,522
Projected benefit obligation at September 30, 2017—Significant Plans	5,665				5,665
Change in plan assets
Plan assets at fair value at beginning of year			6,149		6,149
Plan assets at fair value at September 30, 2017—Significant Plans	5,889				5,889
Funded status of the Significant Plans	224				224
Net amount recognized
Benefit asset	683				683
Benefit liability	(459)				(459)
Net amount recognized on the balance sheet—Significant Plans	224				224
Amounts recognized in AOCI
Prior service benefit	30				30
Net actuarial (loss) gain	(1,051)				(1,051)
Net amount recognized in equity-pretax	(1,021)				(1,021)
Accumulated benefit obligation at September 30, 2017—Significant Plans	5,047				5,047
Non-U.S. plans | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year			1,784		1,784
Change in plan assets
Plan assets at fair value at beginning of year			1,167		1,167
Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	5,549		4,738		4,738
Quarter activity		9	802
Benefits earned during the period	22
Interest cost on benefit obligation	64
Actuarial loss	104
Benefits paid, net of participants’ contributions	(108)
Curtailment loss (gain)	(2)
Foreign exchange impact and other	36
Projected benefit obligation at September 30, 2017—Significant Plans		5,549
Change in plan assets
Plan assets at fair value at beginning of year	5,846		4,982		4,982
Quarter activity		(39)	903
Actual return on plan assets	95
Company contributions, net of reimbursements	11
Plan participants’ contributions	1
Benefits paid, net of government subsidy	(109)
Foreign exchange impact and other	45
Plan assets at fair value at September 30, 2017—Significant Plans		5,846
Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			1,141		1,141
Projected benefit obligation at September 30, 2017—Significant Plans	1,060				1,060
Change in plan assets
Plan assets at fair value at beginning of year			1,015		1,015
Plan assets at fair value at September 30, 2017—Significant Plans	1,186				1,186
Funded status of the Significant Plans	126				126
Net amount recognized
Benefit asset	126				126
Benefit liability	0				0
Net amount recognized on the balance sheet—Significant Plans	126				126
Amounts recognized in AOCI
Prior service benefit	91				91
Net actuarial (loss) gain	(406)				(406)
Net amount recognized in equity-pretax	(315)				(315)
Accumulated benefit obligation at September 30, 2017—Significant Plans	1,060				1,060
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			303		303
Change in plan assets
Plan assets at fair value at beginning of year			11		11
Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	1,044		838		838
Quarter activity		72	134
Benefits earned during the period	2
Interest cost on benefit obligation	23
Actuarial loss	12
Benefits paid, net of participants’ contributions	(15)
Curtailment loss (gain)	0
Foreign exchange impact and other	(6)
Projected benefit obligation at September 30, 2017—Significant Plans		1,044
Change in plan assets
Plan assets at fair value at beginning of year	1,183		1,004		1,004
Quarter activity		55	$ 124
Actual return on plan assets	24
Company contributions, net of reimbursements	0
Plan participants’ contributions	0
Benefits paid, net of government subsidy	(15)
Foreign exchange impact and other	(6)
Plan assets at fair value at September 30, 2017—Significant Plans		$ 1,183
Qualified plans | U.S. | Pension Plans
Change in projected benefit obligation
Benefits earned during the period	0			$ 1	1	$ 2
Interest cost on benefit obligation	124			126	384	399
Change in plan assets
Funded status of the Significant Plans	(575)				(575)
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	13,193				13,193
Qualified plans | U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Benefits earned during the period	0			0	0	0
Interest cost on benefit obligation	9			6	20	19
Change in plan assets
Funded status of the Significant Plans	(611)				(611)
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	736				736
Qualified plans | Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Benefits earned during the period	38			39	112	116
Interest cost on benefit obligation	76			70	221	216
Change in plan assets
Funded status of the Significant Plans	224				224
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	5,047				5,047
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Benefits earned during the period	3			1	7	7
Interest cost on benefit obligation	27			$ 24	76	$ 72
Change in plan assets
Funded status of the Significant Plans	126				126
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	1,060				1,060
Nonqualified plans | U.S. | Pension Plans
Change in plan assets
Funded status of the Significant Plans	(730)				(730)
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	727				727
Nonqualified plans | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the Significant Plans	0				0
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	0				0
Nonqualified plans | Non-U.S. plans | Pension Plans
Change in plan assets
Funded status of the Significant Plans	0				0
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—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
Amounts recognized in AOCI
Accumulated benefit obligation at September 30, 2017—Significant Plans	$ 0				$ 0