RETIREMENT BENEFITS - Fair Value Disclosure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total investments
Defined Benefit Plan Disclosure
Plan assets valued at NAV
U.S.
Defined Benefit Plan Disclosure
Other investment liabilities	$ (403)	$ (659)
Total net assets	12,988	12,492
U.S. | Level 1
Defined Benefit Plan Disclosure
Other investment liabilities	(60)	(106)
U.S. | Level 2
Defined Benefit Plan Disclosure
Other investment liabilities	(343)	(553)
U.S. | Level 3
Defined Benefit Plan Disclosure
Other investment liabilities	0	0
U.S. | U.S. equity
Defined Benefit Plan Disclosure
Total assets	726	639
U.S. | U.S. equity | Level 1
Defined Benefit Plan Disclosure
Total assets	726	639
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	$ 0
U.S. | Non-U.S. equity
Defined Benefit Plan Disclosure
Total assets	926	773
U.S. | Non-U.S. equity | Level 1
Defined Benefit Plan Disclosure
Total assets	926	773
U.S. | Non-U.S. equity | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Non-U.S. equity | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Mutual funds
Defined Benefit Plan Disclosure
Total assets	271	216
U.S. | Mutual funds | Level 1
Defined Benefit Plan Disclosure
Total assets	271	216
U.S. | Mutual funds | Level 2
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Mutual funds | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Commingled funds
Defined Benefit Plan Disclosure
Total assets	1,184	866
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	1,184	866
U.S. | Commingled funds | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Debt securities
Defined Benefit Plan Disclosure
Total assets	4,461	4,142
U.S. | Debt securities | Level 1
Defined Benefit Plan Disclosure
Total assets	1,381	1,297
U.S. | Debt securities | Level 2
Defined Benefit Plan Disclosure
Total assets	3,080	2,845
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	25
U.S. | Derivatives
Defined Benefit Plan Disclosure
Total assets	334	551
U.S. | Derivatives | Level 1
Defined Benefit Plan Disclosure
Total assets	11	8
U.S. | Derivatives | Level 2
Defined Benefit Plan Disclosure
Total assets	323	543
U.S. | Derivatives | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
U.S. | Other investments
Defined Benefit Plan Disclosure
Total assets	22	4
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	22	4	149
U.S. | Total investments
Defined Benefit Plan Disclosure
Total assets	7,925	7,192
Net investments at fair value	8,783	7,888
U.S. | Total investments | Level 1
Defined Benefit Plan Disclosure
Total assets	3,315	2,933
Net investments at fair value	3,512	2,943
U.S. | Total investments | Level 2
Defined Benefit Plan Disclosure
Total assets	4,587	4,254
Net investments at fair value	5,248	4,940
U.S. | Total investments | Level 3
Defined Benefit Plan Disclosure
Total assets	23	5	174
Net investments at fair value	23	5
U.S. | Cash and short-term investments
Defined Benefit Plan Disclosure
Total assets	1,261	1,355
U.S. | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure
Total assets	257	116
U.S. | Cash and short-term investments | Level 2
Defined Benefit Plan Disclosure
Total assets	1,004	1,239
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	16	100
U.S. | Securities
Defined Benefit Plan Disclosure
Plan assets valued at NAV	4,189	4,504
Non-U.S.
Defined Benefit Plan Disclosure
Other investment liabilities	(4,222)	(961)
Total net assets	8,247	7,162
Non-U.S. | Level 1
Defined Benefit Plan Disclosure
Other investment liabilities	(2)	(1)
Non-U.S. | Level 2
Defined Benefit Plan Disclosure
Other investment liabilities	(4,220)	(960)
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	15
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	11
Non-U.S. | U.S. equity | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Non-U.S. equity
Defined Benefit Plan Disclosure
Total assets	226	262
Non-U.S. | Non-U.S. equity | Level 1
Defined Benefit Plan Disclosure
Total assets	103	87
Non-U.S. | Non-U.S. equity | Level 2
Defined Benefit Plan Disclosure
Total assets	122	174
Non-U.S. | Non-U.S. equity | Level 3
Defined Benefit Plan Disclosure
Total assets	1	1	47
Non-U.S. | Mutual funds
Defined Benefit Plan Disclosure
Total assets	3,172	2,751
Non-U.S. | Mutual funds | Level 1
Defined Benefit Plan Disclosure
Total assets	3,098	2,345
Non-U.S. | Mutual funds | Level 2
Defined Benefit Plan Disclosure
Total assets	74	406
Non-U.S. | Mutual funds | Level 3
Defined Benefit Plan Disclosure
Total assets	0	0
Non-U.S. | Commingled funds
Defined Benefit Plan Disclosure
Total assets	24	22
Non-U.S. | Commingled funds | Level 1
Defined Benefit Plan Disclosure
Total assets	24	22
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	5,561	4,619
Non-U.S. | Debt securities | Level 1
Defined Benefit Plan Disclosure
Total assets	3,999	3,406
Non-U.S. | Debt securities | Level 2
Defined Benefit Plan Disclosure
Total assets	1,555	1,206
Non-U.S. | Debt securities | Level 3
Defined Benefit Plan Disclosure
Total assets	7	7	5
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	10	9
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	1	1
Non-U.S. | Annuity contracts | Level 3
Defined Benefit Plan Disclosure
Total assets	9	8	8
Non-U.S. | Derivatives
Defined Benefit Plan Disclosure
Total assets	3,103	43
Non-U.S. | Derivatives | Level 1
Defined Benefit Plan Disclosure
Total assets	1	0
Non-U.S. | Derivatives | Level 2
Defined Benefit Plan Disclosure
Total assets	3,102	43
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	215	188
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	214	187	196
Non-U.S. | Total investments
Defined Benefit Plan Disclosure
Total assets	12,331	7,913
Net investments at fair value	8,231	7,070
Non-U.S. | Total investments | Level 1
Defined Benefit Plan Disclosure
Total assets	7,230	5,865
Net investments at fair value	7,347	5,980
Non-U.S. | Total investments | Level 2
Defined Benefit Plan Disclosure
Total assets	4,869	1,844
Net investments at fair value	652	886
Non-U.S. | Total investments | Level 3
Defined Benefit Plan Disclosure
Total assets	232	204	257
Net investments at fair value	232	204
Non-U.S. | Cash and short-term investments
Defined Benefit Plan Disclosure
Total assets	122	118
Non-U.S. | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure
Total assets	119	116
Non-U.S. | Cash and short-term investments | Level 2
Defined Benefit Plan Disclosure
Total assets	3	2
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	16	92
Pension Plans | U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 12,725	$ 12,363	12,137
Allocable interest (as a percent)	99.00%	99.00%
Pension Plans | Non-U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 7,128	$ 6,149	6,104
Postretirement Benefit Plans | U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 262	$ 129	166
Allocable interest (as a percent)	1.00%	1.00%
Postretirement Benefit Plans | Non-U.S.
Defined Benefit Plan Disclosure
Total net assets	$ 1,119	$ 1,015	$ 1,133