RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
U.S. | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			$ 13,453		$ 13,453
Benefits earned during the period	$ 0			$ 1	0	$ 1
Interest cost on benefit obligation	87			112	294	365
Change in plan assets
Plan assets at fair value at beginning of year			12,717		12,717
Net amount recognized at period end
Benefit asset	0				0
Benefit liability	(1,082)				(1,082)
Net amount recognized on the balance sheet—Significant Plans	(1,082)				(1,082)
Amounts recognized in AOCI at period end
Prior service benefit	0				0
Net actuarial (loss) gain	(7,653)				(7,653)
Net amount recognized in equity-pretax	(7,653)				(7,653)
Accumulated benefit obligation at period end—Significant Plans	13,786				13,786
U.S. | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year			26		26
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	13,860		13,427		13,427
Quarter activity		$ 511	(78)
Benefits earned during the period	0
Interest cost on benefit obligation	87
Actuarial loss (gain)	71
Benefits paid, net of participants’ contributions and government subsidy	(229)
Plan amendments	0
Settlement (gain)	0
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	13,789	13,860			13,789
Change in plan assets
Plan assets at fair value at beginning of year	12,429		12,717		12,717
Quarterly activity		576	(864)
Actual return on plan assets	494
Company contributions, net of reimbursements	13
Benefits paid, net of participants’ contributions and government subsidy	(229)
Settlement gain	0
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	12,707	12,429			12,707
Funded status of the Significant Plans	(1,082)				(1,082)
U.S. | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			692		692
Benefits earned during the period	0			0	0	0
Interest cost on benefit obligation	4			6	14	19
Change in plan assets
Plan assets at fair value at beginning of year			345		345
Net amount recognized at period end
Benefit asset	0				0
Benefit liability	(247)				(247)
Net amount recognized on the balance sheet—Significant Plans	(247)				(247)
Amounts recognized in AOCI at period end
Prior service benefit	104				104
Net actuarial (loss) gain	33				33
Net amount recognized in equity-pretax	137				137
Accumulated benefit obligation at period end—Significant Plans	569				569
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	679		692		692
Quarter activity		0	(13)
Benefits earned during the period	0
Interest cost on benefit obligation	4
Actuarial loss (gain)	1
Benefits paid, net of participants’ contributions and government subsidy	(11)
Plan amendments	(104)
Settlement (gain)	0
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	569	679			569
Change in plan assets
Plan assets at fair value at beginning of year	324		345		345
Quarterly activity		3	(24)
Actual return on plan assets	9
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(11)
Settlement gain	0
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	322	324			322
Funded status of the Significant Plans	(247)				(247)
Non-U.S. plans | Pension Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			8,105		8,105
Benefits earned during the period	38			37	109	108
Interest cost on benefit obligation	59			70	184	218
Change in plan assets
Plan assets at fair value at beginning of year			7,556		7,556
Net amount recognized at period end
Benefit asset	895				895
Benefit liability	(622)				(622)
Net amount recognized on the balance sheet—Significant Plans	273				273
Amounts recognized in AOCI at period end
Prior service benefit	7				7
Net actuarial (loss) gain	(883)				(883)
Net amount recognized in equity-pretax	(876)				(876)
Accumulated benefit obligation at period end—Significant Plans	5,329				5,329
Non-U.S. plans | Pension Plans | Other than Significant Plans Measured Annually
Change in projected benefit obligation
Projected benefit obligation at beginning of year			2,068		2,068
Change in plan assets
Plan assets at fair value at beginning of year			1,349		1,349
Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	5,576		6,037		6,037
Quarter activity		473	(934)
Benefits earned during the period	22
Interest cost on benefit obligation	50
Actuarial loss (gain)	(26)
Benefits paid, net of participants’ contributions and government subsidy	(16)
Plan amendments	0
Settlement (gain)	81
Foreign exchange impact and other	110
Projected benefit obligation at period end—Significant Plans	5,635	5,576			5,635
Change in plan assets
Plan assets at fair value at beginning of year	5,863		6,207		6,207
Quarterly activity		376	(720)
Actual return on plan assets	23
Company contributions, net of reimbursements	18
Benefits paid, net of participants’ contributions and government subsidy	(16)
Settlement gain	(81)
Foreign exchange impact and other	101
Plan assets at fair value at period end—Significant Plans	5,908	5,863			5,908
Funded status of the Significant Plans	273				273
Non-U.S. plans | Postretirement Benefit Plans
Change in projected benefit obligation
Projected benefit obligation at beginning of year			1,384		1,384
Benefits earned during the period	2			2	6	6
Interest cost on benefit obligation	22			$ 25	68	$ 77
Change in plan assets
Plan assets at fair value at beginning of year			1,127		1,127
Net amount recognized at period end
Benefit asset	54				54
Benefit liability	0				0
Net amount recognized on the balance sheet—Significant Plans	54				54
Amounts recognized in AOCI at period end
Prior service benefit	54				54
Net actuarial (loss) gain	(281)				(281)
Net amount recognized in equity-pretax	(227)				(227)
Accumulated benefit obligation at period end—Significant Plans	939				939
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			323		323
Change in plan assets
Plan assets at fair value at beginning of year			9		9
Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in projected benefit obligation
Projected benefit obligation at beginning of year	911		1,061		1,061
Quarter activity		105	(255)
Benefits earned during the period	1
Interest cost on benefit obligation	20
Actuarial loss (gain)	(20)
Benefits paid, net of participants’ contributions and government subsidy	(12)
Plan amendments	0
Settlement (gain)	0
Foreign exchange impact and other	39
Projected benefit obligation at period end—Significant Plans	939	911			939
Change in plan assets
Plan assets at fair value at beginning of year	942		1,118		1,118
Quarterly activity		94	$ (270)
Actual return on plan assets	23
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(12)
Settlement gain	0
Foreign exchange impact and other	40
Plan assets at fair value at period end—Significant Plans	993	$ 942			993
Funded status of the Significant Plans	54				54
Qualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(369)				(369)
Qualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(247)				(247)
Qualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	273				273
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	54				54
Nonqualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(713)				(713)
Nonqualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	0				0
Nonqualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	0				0
Nonqualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	$ 0				$ 0