RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in projected benefit obligation
Interest cost on benefit obligation	$ 2	$ 3	$ 4
Actuarial loss (gain)	2	5	12
U.S.
Change in plan assets
Plan assets at fair value at beginning of year	12,492
Plan assets at fair value at year end	12,988	12,492
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	14,000	13,943
Benefits earned during the year	3	4	6
Interest cost on benefit obligation	533	548	581
Plan amendments	0	0
Actuarial loss (gain)	536	367
Benefits paid, net of participants’ contributions and government subsidy	(769)	(780)
Divestitures	0	0
Settlement gain	0	0
Curtailment (gain) loss	6	13
Foreign exchange impact and other	(269)	(95)
Projected benefit obligation at period end	14,040	14,000	13,943
Change in plan assets
Plan assets at fair value at beginning of year	12,363	12,137
Actual return on plan assets	1,295	572
Company contributions	105	556
Divestitures	0	0
Settlements	0	0
Benefits paid, net of participants’ contributions and government subsidy	(769)	(779)
Foreign exchange impact and other	(269)	(123)
Plan assets at fair value at year end	12,725	12,363	12,137
Funded status of the plans	(1,315)	(1,637)
Net amount recognized
Net amount recognized on the balance sheet	(1,315)	(1,637)
Amounts recognized in Accumulated other comprehensive income (loss)
Net transition obligation	0	0
Prior service benefit	(15)	(17)
Net actuarial gain (loss)	(6,823)	(6,891)
Net amount recognized in equity-pretax	(6,838)	(6,908)
Accumulated benefit obligation at period end	14,034	13,994
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	686	817
Benefits earned during the year	0	0	0
Interest cost on benefit obligation	26	25	33
Plan amendments	0	0
Actuarial loss (gain)	43	(105)
Benefits paid, net of participants’ contributions and government subsidy	(56)	(51)
Divestitures	0	0
Settlement gain	0	0
Curtailment (gain) loss	0	0
Foreign exchange impact and other	0	0
Projected benefit obligation at period end	699	686	817
Change in plan assets
Plan assets at fair value at beginning of year	129	166
Actual return on plan assets	13	8
Company contributions	176	6
Divestitures	0	0
Settlements	0	0
Benefits paid, net of participants’ contributions and government subsidy	(56)	(51)
Foreign exchange impact and other	0	0
Plan assets at fair value at year end	262	129	166
Funded status of the plans	(437)	(557)
Net amount recognized
Net amount recognized on the balance sheet	(437)	(557)
Amounts recognized in Accumulated other comprehensive income (loss)
Net transition obligation	0	0
Prior service benefit	0	0
Net actuarial gain (loss)	72	106
Net amount recognized in equity-pretax	72	106
Accumulated benefit obligation at period end	699	686
Non-U.S.
Change in plan assets
Plan assets at fair value at beginning of year	7,162
Plan assets at fair value at year end	8,247	7,162
Non-U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	6,522	6,534
Benefits earned during the year	153	154	168
Interest cost on benefit obligation	295	282	317
Plan amendments	4	(28)
Actuarial loss (gain)	127	589
Benefits paid, net of participants’ contributions and government subsidy	(278)	(324)
Divestitures	(29)	(22)
Settlement gain	(192)	(38)
Curtailment (gain) loss	(3)	(15)
Foreign exchange impact and other	834	(610)
Projected benefit obligation at period end	7,433	6,522	6,534
Change in plan assets
Plan assets at fair value at beginning of year	6,149	6,104
Actual return on plan assets	462	967
Company contributions	135	126
Divestitures	(31)	(5)
Settlements	(192)	(38)
Benefits paid, net of participants’ contributions and government subsidy	(278)	(324)
Foreign exchange impact and other	883	(681)
Plan assets at fair value at year end	7,128	6,149	6,104
Funded status of the plans	(305)	(373)
Net amount recognized
Net amount recognized on the balance sheet	(305)	(373)
Amounts recognized in Accumulated other comprehensive income (loss)
Net transition obligation	(1)	(1)
Prior service benefit	22	29
Net actuarial gain (loss)	(1,318)	(1,302)
Net amount recognized in equity-pretax	(1,297)	(1,274)
Accumulated benefit obligation at period end	7,038	6,090
Non-U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	1,141	1,291
Benefits earned during the year	9	10	12
Interest cost on benefit obligation	101	94	108
Plan amendments	0	0
Actuarial loss (gain)	19	3
Benefits paid, net of participants’ contributions and government subsidy	(64)	(59)
Divestitures	(4)	0
Settlement gain	0	0
Curtailment (gain) loss	0	(4)
Foreign exchange impact and other	59	(194)
Projected benefit obligation at period end	1,261	1,141	1,291
Change in plan assets
Plan assets at fair value at beginning of year	1,015	1,133
Actual return on plan assets	113	122
Company contributions	9	9
Divestitures	0	0
Settlements	0	0
Benefits paid, net of participants’ contributions and government subsidy	(64)	(59)
Foreign exchange impact and other	46	(190)
Plan assets at fair value at year end	1,119	1,015	$ 1,133
Funded status of the plans	(142)	(126)
Net amount recognized
Net amount recognized on the balance sheet	(142)	(126)
Amounts recognized in Accumulated other comprehensive income (loss)
Net transition obligation	0	0
Prior service benefit	92	98
Net actuarial gain (loss)	(382)	(399)
Net amount recognized in equity-pretax	(290)	(301)
Accumulated benefit obligation at period end	1,261	1,141
Qualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(565)	(908)
Net amount recognized
Benefit asset	0	0
Benefit liability	(565)	(908)
Net amount recognized on the balance sheet	(565)	(908)
Qualified | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(437)	(557)
Net amount recognized
Benefit asset	0	0
Benefit liability	(437)	(557)
Net amount recognized on the balance sheet	(437)	(557)
Qualified | Non-U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(305)	(373)
Net amount recognized
Benefit asset	900	711
Benefit liability	(1,205)	(1,084)
Net amount recognized on the balance sheet	(305)	(373)
Qualified | Non-U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(142)	(126)
Net amount recognized
Benefit asset	181	166
Benefit liability	(323)	(292)
Net amount recognized on the balance sheet	(142)	(126)
Nonqualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(750)	(729)
Net amount recognized
Net amount recognized on the balance sheet	(750)	(729)
Nonqualified | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	0	0
Net amount recognized
Net amount recognized on the balance sheet	0	0
Nonqualified | Non-U.S. | Pension Plans
Change in plan assets
Funded status of the plans	0	0
Net amount recognized
Net amount recognized on the balance sheet	0	0
Nonqualified | Non-U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	0	0
Net amount recognized
Net amount recognized on the balance sheet	$ 0	$ 0