RETIREMENT BENEFITS - Net (Benefit) Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
U.S. | Pension Plans
Service-related expense
Benefits earned during the period	$ 0	$ 0	$ 1	$ 1
Interest cost on benefit obligation	126	136	249	275
Expected return on plan assets	(211)	(217)	(424)	(433)
Amortization of unrecognized
Prior service benefit	0	1	0	1
Net actuarial loss	42	40	89	84
Curtailment loss	1	3	1	3
Settlement loss	0	0	0	0
Total net (benefit) expense	(42)	(37)	(84)	(69)
U.S. | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	0	0	0	0
Interest cost on benefit obligation	7	8	13	14
Expected return on plan assets	(3)	(2)	(6)	(3)
Amortization of unrecognized
Prior service benefit	0	0	0	0
Net actuarial loss	0	1	0	0
Curtailment loss	0	0	0	0
Settlement loss	0	0	0	0
Total net (benefit) expense	4	7	7	11
Non-U.S. plans | Pension Plans
Service-related expense
Benefits earned during the period	38	38	76	74
Interest cost on benefit obligation	72	74	147	145
Expected return on plan assets	(72)	(76)	(150)	(146)
Amortization of unrecognized
Prior service benefit	(1)	(1)	(2)	(2)
Net actuarial loss	14	15	27	31
Curtailment loss	0	0	0	0
Settlement loss	1	4	5	4
Total net (benefit) expense	52	54	103	106
Non-U.S. plans | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	3	2	5	4
Interest cost on benefit obligation	25	25	51	49
Expected return on plan assets	(22)	(22)	(45)	(43)
Amortization of unrecognized
Prior service benefit	(3)	(3)	(5)	(5)
Net actuarial loss	8	9	15	17
Curtailment loss	0	0	0	0
Settlement loss	0	0	0	0
Total net (benefit) expense	$ 11	$ 11	$ 21	$ 22