RETIREMENT BENEFITS - Net (Benefit) Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
U.S. | Pension Plans
Service-related expense
Benefits earned during the period	$ 1	$ 1
Interest cost on benefit obligation	123	139
Expected return on plan assets	(213)	(216)
Amortization of unrecognized
Prior service benefit	0	0
Net actuarial loss (gain)	47	44
Settlement loss	0	0
Total net (benefit) expense	(42)	(32)
U.S. | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	0	0
Interest cost on benefit obligation	6	6
Expected return on plan assets	(3)	(1)
Amortization of unrecognized
Prior service benefit	0	0
Net actuarial loss (gain)	0	(1)
Settlement loss	0	0
Total net (benefit) expense	3	4
Non-U.S. plans | Pension Plans
Service-related expense
Benefits earned during the period	38	36
Interest cost on benefit obligation	75	71
Expected return on plan assets	(78)	(70)
Amortization of unrecognized
Prior service benefit	(1)	(1)
Net actuarial loss (gain)	13	16
Settlement loss	4	0
Total net (benefit) expense	51	52
Non-U.S. plans | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	2	2
Interest cost on benefit obligation	26	24
Expected return on plan assets	(23)	(21)
Amortization of unrecognized
Prior service benefit	(2)	(2)
Net actuarial loss (gain)	7	8
Settlement loss	0	0
Total net (benefit) expense	$ 10	$ 11