RETIREMENT BENEFITS - Net (Benefit) Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
U.S. | Pension Plans
Service-related expense
Benefits earned during the period	$ 0	$ 1
Interest cost on benefit obligation	130	123
Expected return on plan assets	(203)	(213)
Amortization of unrecognized:
Prior service cost (benefit)	1	0
Net actuarial loss	44	47
Settlement loss	0	0
Total net (benefit) expense	(28)	(42)
U.S. | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	0	0
Interest cost on benefit obligation	7	6
Expected return on plan assets	(5)	(3)
Amortization of unrecognized:
Prior service cost (benefit)	0	0
Net actuarial loss	0	0
Settlement loss	0	0
Total net (benefit) expense	2	3
Non-U.S. plans | Pension Plans
Service-related expense
Benefits earned during the period	36	38
Interest cost on benefit obligation	75	75
Expected return on plan assets	(68)	(78)
Amortization of unrecognized:
Prior service cost (benefit)	(1)	(1)
Net actuarial loss	15	13
Settlement loss	0	4
Total net (benefit) expense	57	51
Non-U.S. plans | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	2	2
Interest cost on benefit obligation	26	26
Expected return on plan assets	(21)	(23)
Amortization of unrecognized:
Prior service cost (benefit)	(2)	(2)
Net actuarial loss	5	7
Settlement loss	0	0
Total net (benefit) expense	$ 10	$ 10