RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in projected benefit obligation
Interest cost on benefit obligation	$ 2	$ 2	$ 2
Actuarial loss (gain)	2	2	2
Amounts recognized in AOCI
Net amount recognized in equity-pretax	15	15
Subsidy received under the EGWP	22	15
U.S.
Change in plan assets
Plan assets at fair value at beginning of year	11,835
Plan assets at fair value at year end	13,062	11,835
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	12,655	14,040
Benefits earned during the year	1	1	3
Interest cost on benefit obligation	469	514	533
Plan amendments	0	0
Actuarial loss (gain)	1,263	(1,056)
Benefits paid, net of participants’ contributions and government subsidy	(936)	(845)
Settlement gain	0
Curtailment loss (gain)	1	1
Foreign exchange impact and other	0	0
Projected benefit obligation at period end	13,453	12,655	14,040
Change in plan assets
Plan assets at fair value at beginning of year	11,490	12,725
Actual return on plan assets	1,682	(445)
Company contributions	481	55
Benefits paid, net of participants’ contributions and government subsidy	(936)	(845)
Settlement	0	0
Foreign exchange impact and other	0	0
Plan assets at fair value at year end	12,717	11,490	12,725
Funded status of the plans	(736)	(1,165)
Net amount recognized
Net amount recognized on the balance sheet	(736)	(1,165)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service (cost) benefit	(12)	(13)
Net actuarial (loss) gain	(7,092)	(6,892)
Net amount recognized in equity-pretax	(7,104)	(6,905)
Accumulated benefit obligation at period end	13,447	12,646
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	662	699
Benefits earned during the year	0	0	0
Interest cost on benefit obligation	24	26	26
Plan amendments	0	0
Actuarial loss (gain)	46	(1)
Benefits paid, net of participants’ contributions and government subsidy	(40)	(62)
Settlement gain	0	0
Curtailment loss (gain)	0	0
Foreign exchange impact and other	0	0
Projected benefit obligation at period end	692	662	699
Change in plan assets
Plan assets at fair value at beginning of year	345	262
Actual return on plan assets	36	(5)
Company contributions	4	150
Benefits paid, net of participants’ contributions and government subsidy	(40)	(62)
Settlement	0	0
Foreign exchange impact and other	0	0
Plan assets at fair value at year end	345	345	262
Funded status of the plans	(347)	(317)
Net amount recognized
Net amount recognized on the balance sheet	(347)	(317)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service (cost) benefit	0	0
Net actuarial (loss) gain	24	53
Net amount recognized in equity-pretax	24	53
Accumulated benefit obligation at period end	692	662
Non-U.S.
Change in plan assets
Plan assets at fair value at beginning of year	7,735
Plan assets at fair value at year end	8,683	7,735
Non-U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	7,149	7,433
Benefits earned during the year	146	146	153
Interest cost on benefit obligation	287	292	295
Plan amendments	7	7
Actuarial loss (gain)	861	(99)
Benefits paid, net of participants’ contributions and government subsidy	(304)	(293)
Settlement gain	(84)	(121)
Curtailment loss (gain)	(4)	(1)
Foreign exchange impact and other	47	(215)
Projected benefit obligation at period end	8,105	7,149	7,433
Change in plan assets
Plan assets at fair value at beginning of year	6,699	7,128
Actual return on plan assets	781	(11)
Company contributions	150	182
Benefits paid, net of participants’ contributions and government subsidy	(304)	(293)
Settlement	(84)	(121)
Foreign exchange impact and other	314	(186)
Plan assets at fair value at year end	7,556	6,699	7,128
Funded status of the plans	(549)	(450)
Net amount recognized
Net amount recognized on the balance sheet	(549)	(450)
Amounts recognized in AOCI
Net transition obligation	0	(1)
Prior service (cost) benefit	1	12
Net actuarial (loss) gain	(1,735)	(1,420)
Net amount recognized in equity-pretax	(1,734)	(1,409)
Accumulated benefit obligation at period end	7,618	6,720
Non-U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year	1,159	1,261
Benefits earned during the year	8	9	9
Interest cost on benefit obligation	104	102	101
Plan amendments	0	0
Actuarial loss (gain)	140	(123)
Benefits paid, net of participants’ contributions and government subsidy	(72)	(68)
Settlement gain	0	0
Curtailment loss (gain)	0	0
Foreign exchange impact and other	45	(22)
Projected benefit obligation at period end	1,384	1,159	1,261
Change in plan assets
Plan assets at fair value at beginning of year	1,036	1,119
Actual return on plan assets	138	(26)
Company contributions	225	9
Benefits paid, net of participants’ contributions and government subsidy	(72)	(68)
Settlement	0	0
Foreign exchange impact and other	(200)	2
Plan assets at fair value at year end	1,127	1,036	$ 1,119
Funded status of the plans	(257)	(123)
Net amount recognized
Net amount recognized on the balance sheet	(257)	(123)
Amounts recognized in AOCI
Net transition obligation	0	0
Prior service (cost) benefit	76	83
Net actuarial (loss) gain	(416)	(340)
Net amount recognized in equity-pretax	(340)	(257)
Accumulated benefit obligation at period end	1,384	1,159
Qualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(23)	(483)
Net amount recognized
Benefit asset	0	0
Benefit liability	(23)	(483)
Net amount recognized on the balance sheet	(23)	(483)
Qualified | U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(347)	(317)
Net amount recognized
Benefit asset	0	0
Benefit liability	(347)	(317)
Net amount recognized on the balance sheet	(347)	(317)
Qualified | Non-U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(549)	(450)
Net amount recognized
Benefit asset	808	806
Benefit liability	(1,357)	(1,256)
Net amount recognized on the balance sheet	(549)	(450)
Qualified | Non-U.S. | Postretirement Benefit Plans
Change in plan assets
Funded status of the plans	(257)	(123)
Net amount recognized
Benefit asset	57	175
Benefit liability	(314)	(298)
Net amount recognized on the balance sheet	(257)	(123)
Nonqualified | U.S. | Pension Plans
Change in plan assets
Funded status of the plans	(713)	(682)
Net amount recognized
Net amount recognized on the balance sheet	(713)	(682)
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