RETIREMENT BENEFITS - Funded Status and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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		$ 0	0	$ 0
Interest cost on benefit obligation	101		123	207	253
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	(1,431)			(1,431)
Net amount recognized on the balance sheet—Significant Plans	(1,431)			(1,431)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	(7,933)			(7,933)
Net amount recognized in equity-pretax	(7,933)			(7,933)
Accumulated benefit obligation at period end—Significant Plans	13,857			13,857
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	13,349	13,427		13,427
Quarter activity		(78)
Benefits earned during the period
Interest cost on benefit obligation	101
Actuarial loss	678
Benefits paid, net of participants’ contributions and government subsidy	(268)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	13,860	13,349		13,860
Change in plan assets
Plan assets at fair value at beginning of year	11,853	12,717		12,717
Quarterly activity		(864)
Actual return on plan assets	830
Company contributions, net of reimbursements	14
Benefits paid, net of participants’ contributions and government subsidy	(268)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	12,429	11,853		12,429
Funded status of the Significant Plans	(1,431)			(1,431)
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	5		6	10	13
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	(355)			(355)
Net amount recognized on the balance sheet—Significant Plans	(355)			(355)
Amounts recognized in AOCI at period end
Prior service benefit	0			0
Net actuarial (loss) gain	29			29
Net amount recognized in equity-pretax	29			29
Accumulated benefit obligation at period end—Significant Plans	679			679
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		(13)
Benefits earned during the period	0
Interest cost on benefit obligation	5
Actuarial loss	5
Benefits paid, net of participants’ contributions and government subsidy	(10)
Foreign exchange impact and other	0
Projected benefit obligation at period end—Significant Plans	679	679		679
Change in plan assets
Plan assets at fair value at beginning of year	321	345		345
Quarterly activity		(24)
Actual return on plan assets	16
Company contributions, net of reimbursements	(3)
Benefits paid, net of participants’ contributions and government subsidy	(10)
Foreign exchange impact and other	0
Plan assets at fair value at period end—Significant Plans	324	321		324
Funded status of the Significant Plans	(355)			(355)
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	34		35	71	71
Interest cost on benefit obligation	61		73	125	148
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	907			907
Benefit liability	(620)			(620)
Net amount recognized on the balance sheet—Significant Plans	287			287
Amounts recognized in AOCI at period end
Prior service benefit	8			8
Net actuarial (loss) gain	(854)			(854)
Net amount recognized in equity-pretax	(846)			(846)
Accumulated benefit obligation at period end—Significant Plans	5,283			5,283
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	5,103	6,037		6,037
Quarter activity		(934)
Benefits earned during the period	20
Interest cost on benefit obligation	51
Actuarial loss	466
Benefits paid, net of participants’ contributions and government subsidy	(83)
Foreign exchange impact and other	19
Projected benefit obligation at period end—Significant Plans	5,576	5,103		5,576
Change in plan assets
Plan assets at fair value at beginning of year	5,487	6,207		6,207
Quarterly activity		(720)
Actual return on plan assets	439
Company contributions, net of reimbursements	15
Benefits paid, net of participants’ contributions and government subsidy	(83)
Foreign exchange impact and other	5
Plan assets at fair value at period end—Significant Plans	5,863	5,487		5,863
Funded status of the Significant Plans	287			287
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	4	4
Interest cost on benefit obligation	22		$ 26	46	$ 52
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	31			31
Benefit liability	0			0
Net amount recognized on the balance sheet—Significant Plans	31			31
Amounts recognized in AOCI at period end
Prior service benefit	53			53
Net actuarial (loss) gain	(296)			(296)
Net amount recognized in equity-pretax	(243)			(243)
Accumulated benefit obligation at period end—Significant Plans	911			911
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	806	1,061		1,061
Quarter activity		(255)
Benefits earned during the period	1
Interest cost on benefit obligation	19
Actuarial loss	84
Benefits paid, net of participants’ contributions and government subsidy	(13)
Foreign exchange impact and other	14
Projected benefit obligation at period end—Significant Plans	911	806		911
Change in plan assets
Plan assets at fair value at beginning of year	848	1,118		1,118
Quarterly activity		(270)
Actual return on plan assets	94
Company contributions, net of reimbursements	0
Benefits paid, net of participants’ contributions and government subsidy	(13)
Foreign exchange impact and other	13
Plan assets at fair value at period end—Significant Plans	942	$ 848		942
Funded status of the Significant Plans	31			31
Qualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(713)			(713)
Qualified plans | U.S. | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(355)			(355)
Qualified plans | Non-U.S. plans | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	287			287
Qualified plans | Non-U.S. plans | Postretirement Benefit Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	31			31
Nonqualified plans | U.S. | Pension Plans | Significant Plans Measured Quarterly
Change in plan assets
Funded status of the Significant Plans	(718)			(718)
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