RETIREMENT BENEFITS - Fair Value Disclosure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
U.S.
Defined Benefit Plan Disclosure
Other investment liabilities	$ (336)	$ (354)
Total net assets	13,062	11,835
U.S. | Level 1
Defined Benefit Plan Disclosure
Other investment liabilities	(87)	(100)
U.S. | Level 2
Defined Benefit Plan Disclosure
Other investment liabilities	(249)	(254)
U.S. | Level 3
Defined Benefit Plan Disclosure
Other investment liabilities	0	0
U.S. | U.S. equity
Defined Benefit Plan Disclosure
Total assets	739	625
U.S. | U.S. equity | Level 1
Defined Benefit Plan Disclosure
Total assets	739	625
U.S. | U.S. equity | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | U.S. equity | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Non-U.S. equities
Defined Benefit Plan Disclosure
Total assets	553	481
U.S. | Non-U.S. equities | Level 1
Defined Benefit Plan Disclosure
Total assets	553	481
U.S. | Non-U.S. equities | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Non-U.S. equities | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Mutual funds and other registered investment companies
Defined Benefit Plan Disclosure
Total assets	280	215
U.S. | Mutual funds and other registered investment companies | Level 1
Defined Benefit Plan Disclosure
Total assets	280	215
U.S. | Mutual funds and other registered investment companies | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Mutual funds and other registered investment companies | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Commingled funds
Defined Benefit Plan Disclosure
Total assets	1,410	1,344
U.S. | Commingled funds | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Commingled funds | Level 2
Defined Benefit Plan Disclosure
Total assets	1,410	1,344
U.S. | Commingled funds | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Debt securities
Defined Benefit Plan Disclosure
Total assets	5,580	4,789
U.S. | Debt securities | Level 1
Defined Benefit Plan Disclosure
Total assets	1,534	1,346
U.S. | Debt securities | Level 2
Defined Benefit Plan Disclosure
Total assets	4,046	3,443
U.S. | Debt securities | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Annuity contracts
Defined Benefit Plan Disclosure
Total assets	1	1
U.S. | Annuity contracts | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Annuity contracts | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Annuity contracts | Level 3
Defined Benefit Plan Disclosure
Total assets	1	1	$ 1
U.S. | Derivatives
Defined Benefit Plan Disclosure
Total assets	255	268
U.S. | Derivatives | Level 1
Defined Benefit Plan Disclosure
Total assets	10	16
U.S. | Derivatives | Level 2
Defined Benefit Plan Disclosure
Total assets	245	252
U.S. | Derivatives | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Other investments
Defined Benefit Plan Disclosure
Total assets	75	127
U.S. | Other investments | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Other investments | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Other investments | Level 3
Defined Benefit Plan Disclosure
Total assets	75	127	148
U.S. | Total investments
Defined Benefit Plan Disclosure
Total assets	8,893	7,850
Net investments at fair value	9,730	8,486
U.S. | Total investments | Level 1
Defined Benefit Plan Disclosure
Total assets	3,116	2,683
Net investments at fair value	3,122	2,676
U.S. | Total investments | Level 2
Defined Benefit Plan Disclosure
Total assets	5,701	5,039
Net investments at fair value	6,532	5,682
U.S. | Total investments | Level 3
Defined Benefit Plan Disclosure
Total assets	76	128	149
Net investments at fair value	76	128
U.S. | Cash and short-term investments
Defined Benefit Plan Disclosure
Total assets	1,173	990
U.S. | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure
Total assets	93	93
U.S. | Cash and short-term investments | Level 2
Defined Benefit Plan Disclosure
Total assets	1,080	897
U.S. | Cash and short-term investments | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Other investment receivables
Defined Benefit Plan Disclosure
Plan assets valued at NAV	22	80
U.S. | Securities
Defined Benefit Plan Disclosure
Plan assets valued at NAV	3,310	3,269
Non-U.S.
Defined Benefit Plan Disclosure
Other investment liabilities	(2,941)	(2,590)
Total net assets	8,683	7,735
Non-U.S. | Level 1
Defined Benefit Plan Disclosure
Other investment liabilities	(3)	(1)
Non-U.S. | Level 2
Defined Benefit Plan Disclosure
Other investment liabilities	(2,938)	(2,589)
Non-U.S. | Level 3
Defined Benefit Plan Disclosure
Other investment liabilities	0	0
Non-U.S. | U.S. equity
Defined Benefit Plan Disclosure
Total assets	16	13
Non-U.S. | U.S. equity | Level 1
Defined Benefit Plan Disclosure
Total assets	4	4
Non-U.S. | U.S. equity | Level 2
Defined Benefit Plan Disclosure
Total assets	12	9
Non-U.S. | U.S. equity | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Non-U.S. equities
Defined Benefit Plan Disclosure
Total assets	389	200
Non-U.S. | Non-U.S. equities | Level 1
Defined Benefit Plan Disclosure
Total assets	127	100
Non-U.S. | Non-U.S. equities | Level 2
Defined Benefit Plan Disclosure
Total assets	262	100
Non-U.S. | Non-U.S. equities | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0	1
Non-U.S. | Mutual funds and other registered investment companies
Defined Benefit Plan Disclosure
Total assets	3,286	2,950
Non-U.S. | Mutual funds and other registered investment companies | Level 1
Defined Benefit Plan Disclosure
Total assets	3,223	2,887
Non-U.S. | Mutual funds and other registered investment companies | Level 2
Defined Benefit Plan Disclosure
Total assets	63	63
Non-U.S. | Mutual funds and other registered investment companies | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Commingled funds
Defined Benefit Plan Disclosure
Total assets	23	21
Non-U.S. | Commingled funds | Level 1
Defined Benefit Plan Disclosure
Total assets	23	21
Non-U.S. | Commingled funds | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Commingled funds | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Debt securities
Defined Benefit Plan Disclosure
Total assets	5,932	6,654
Non-U.S. | Debt securities | Level 1
Defined Benefit Plan Disclosure
Total assets	4,307	5,145
Non-U.S. | Debt securities | Level 2
Defined Benefit Plan Disclosure
Total assets	1,615	1,500
Non-U.S. | Debt securities | Level 3
Defined Benefit Plan Disclosure
Total assets	10	9	7
Non-U.S. | Real estate
Defined Benefit Plan Disclosure
Total assets	4	4
Non-U.S. | Real estate | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Real estate | Level 2
Defined Benefit Plan Disclosure
Total assets	3	3
Non-U.S. | Real estate | Level 3
Defined Benefit Plan Disclosure
Total assets	1	1	1
Non-U.S. | Annuity contracts
Defined Benefit Plan Disclosure
Total assets	5	11
Non-U.S. | Annuity contracts | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Annuity contracts | Level 2
Defined Benefit Plan Disclosure
Total assets	0	1
Non-U.S. | Annuity contracts | Level 3
Defined Benefit Plan Disclosure
Total assets	5	10	9
Non-U.S. | Derivatives
Defined Benefit Plan Disclosure
Total assets	1,590	156
Non-U.S. | Derivatives | Level 1
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Derivatives | Level 2
Defined Benefit Plan Disclosure
Total assets	1,590	156
Non-U.S. | Derivatives | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Other investments
Defined Benefit Plan Disclosure
Total assets	275	211
Non-U.S. | Other investments | Level 1
Defined Benefit Plan Disclosure
Total assets	1	1
Non-U.S. | Other investments | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Other investments | Level 3
Defined Benefit Plan Disclosure
Total assets	274	210	214
Non-U.S. | Total investments
Defined Benefit Plan Disclosure
Total assets	11,520	10,220
Net investments at fair value	8,668	7,724
Non-U.S. | Total investments | Level 1
Defined Benefit Plan Disclosure
Total assets	7,685	8,158
Net investments at fair value	7,768	8,248
Non-U.S. | Total investments | Level 2
Defined Benefit Plan Disclosure
Total assets	3,545	1,832
Net investments at fair value	610	(754)
Non-U.S. | Total investments | Level 3
Defined Benefit Plan Disclosure
Total assets	290	230	232
Net investments at fair value	290	230
Non-U.S. | Cash and short-term investments
Defined Benefit Plan Disclosure
Total assets	89	94
Non-U.S. | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure
Total assets	86	91
Non-U.S. | Cash and short-term investments | Level 2
Defined Benefit Plan Disclosure
Total assets	3	3
Non-U.S. | Cash and short-term investments | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Securities
Defined Benefit Plan Disclosure
Plan assets valued at NAV	15	11
Pension Plans | U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 12,717	$ 11,490	12,725
Allocable interest (as a percent)	98.00%	98.00%
Pension Plans | Non-U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 7,556	$ 6,699	7,128
Postretirement Benefit Plans | U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 345	$ 345	262
Allocable interest (as a percent)	2.00%	2.00%
Postretirement Benefit Plans | Non-U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 1,127	$ 1,036	$ 1,119