RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in projected benefit obligation
Interest cost on benefit obligation	$ 2	$ 2	$ 3
Actuarial loss (gain)	2	2	5
Amounts recognized in AOCI
Net amount recognized in equity-pretax	15	(3)
Subsidy received under the EGWP	15	15
U.S.
Change in plan assets
Plan assets at fair value at beginning of year	12,987
Plan assets at fair value at year end	11,835	12,987
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	14,040	14,000
Benefits earned during the year	1	3	4
Interest cost on benefit obligation	514	533	548
Plan amendments	0	0
Actuarial loss (gain)	(1,056)	536
Benefits paid, net of participants’ contributions and government subsidy	(845)	(769)
Divestitures	0	0
Settlement gain	0	0
Curtailment loss (gain)	1	6
Foreign exchange impact and other	0	(269)
Projected benefit obligation at period end	12,655	14,040	14,000
Change in plan assets
Plan assets at fair value at beginning of year	12,725	12,363
Actual return on plan assets	(445)	1,295
Company contributions	55	105
Benefits paid, net of participants’ contributions and government subsidy	(845)	(769)
Divestitures	0	0
Settlement	0	0
Foreign exchange impact and other	0	(269)
Plan assets at fair value at year end	11,490	12,725	12,363
Funded status of the plans	(1,165)	(1,315)
Net amount recognized
Net amount recognized on the balance sheet	(1,165)	(1,315)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service benefit	(13)	(15)
Net actuarial (loss) gain	(6,892)	(6,823)
Net amount recognized in equity-pretax	(6,905)	(6,838)
Accumulated benefit obligation at period end	12,646	14,034
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	699	686
Benefits earned during the year	0	0	0
Interest cost on benefit obligation	26	26	25
Plan amendments	0	0
Actuarial loss (gain)	(1)	43
Benefits paid, net of participants’ contributions and government subsidy	(62)	(56)
Divestitures	0	0
Settlement gain	0	0
Curtailment loss (gain)	0	0
Foreign exchange impact and other	0	0
Projected benefit obligation at period end	662	699	686
Change in plan assets
Plan assets at fair value at beginning of year	262	129
Actual return on plan assets	(5)	13
Company contributions	150	176
Benefits paid, net of participants’ contributions and government subsidy	(62)	(56)
Divestitures	0	0
Settlement	0	0
Foreign exchange impact and other	0	0
Plan assets at fair value at year end	345	262	129
Funded status of the plans	(317)	(437)
Net amount recognized
Net amount recognized on the balance sheet	(317)	(437)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service benefit	0	0
Net actuarial (loss) gain	53	72
Net amount recognized in equity-pretax	53	72
Accumulated benefit obligation at period end	662	699
Non-U.S.
Change in plan assets
Plan assets at fair value at beginning of year	8,247
Plan assets at fair value at year end	7,735	8,247
Non-U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	7,433	6,522
Benefits earned during the year	146	153	154
Interest cost on benefit obligation	292	295	282
Plan amendments	7	4
Actuarial loss (gain)	(99)	127
Benefits paid, net of participants’ contributions and government subsidy	(293)	(278)
Divestitures	0	(29)
Settlement gain	(121)	(192)
Curtailment loss (gain)	(1)	(3)
Foreign exchange impact and other	(215)	834
Projected benefit obligation at period end	7,149	7,433	6,522
Change in plan assets
Plan assets at fair value at beginning of year	7,128	6,149
Actual return on plan assets	(11)	462
Company contributions	182	135
Benefits paid, net of participants’ contributions and government subsidy	(293)	(278)
Divestitures	0	(31)
Settlement	(121)	(192)
Foreign exchange impact and other	(186)	883
Plan assets at fair value at year end	6,699	7,128	6,149
Funded status of the plans	(450)	(305)
Net amount recognized
Net amount recognized on the balance sheet	(450)	(305)
Amounts recognized in AOCI
Net transition obligation	(1)	(1)
Prior service benefit	12	22
Net actuarial (loss) gain	(1,420)	(1,318)
Net amount recognized in equity-pretax	(1,409)	(1,297)
Accumulated benefit obligation at period end	6,720	7,038
Non-U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	1,261	1,141
Benefits earned during the year	9	9	10
Interest cost on benefit obligation	102	101	94
Plan amendments	0	0
Actuarial loss (gain)	(123)	19
Benefits paid, net of participants’ contributions and government subsidy	(68)	(64)
Divestitures	0	(4)
Settlement gain	0	0
Curtailment loss (gain)	0	0
Foreign exchange impact and other	(22)	59
Projected benefit obligation at period end	1,159	1,261	1,141
Change in plan assets
Plan assets at fair value at beginning of year	1,119	1,015
Actual return on plan assets	(26)	113
Company contributions	9	9
Benefits paid, net of participants’ contributions and government subsidy	(68)	(64)
Divestitures	0	0
Settlement	0	0
Foreign exchange impact and other	2	46
Plan assets at fair value at year end	1,036	1,119	$ 1,015
Funded status of the plans	(123)	(142)
Net amount recognized
Net amount recognized on the balance sheet	(123)	(142)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service benefit	83	92
Net actuarial (loss) gain	(340)	(382)
Net amount recognized in equity-pretax	(257)	(290)
Accumulated benefit obligation at period end	1,159	1,261
Qualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(483)	(565)
Net amount recognized
Benefit asset	0	0
Benefit liability	(483)	(565)
Net amount recognized on the balance sheet	(483)	(565)
Qualified | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(317)	(437)
Net amount recognized
Benefit asset	0	0
Benefit liability	(317)	(437)
Net amount recognized on the balance sheet	(317)	(437)
Qualified | Non-U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(450)	(305)
Net amount recognized
Benefit asset	806	900
Benefit liability	(1,256)	(1,205)
Net amount recognized on the balance sheet	(450)	(305)
Qualified | Non-U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(123)	(142)
Net amount recognized
Benefit asset	175	181
Benefit liability	(298)	(323)
Net amount recognized on the balance sheet	(123)	(142)
Nonqualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(682)	(750)
Net amount recognized
Net amount recognized on the balance sheet	(682)	(750)
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