RETIREMENT BENEFITS - Net (Benefit) Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
U.S. | Pension Plans
Service-related expense
Benefits earned during the period	$ 0	$ 0
Interest cost on benefit obligation	106	130
Expected return on plan assets	(208)	(203)
Amortization of unrecognized:
Prior service cost (benefit)	1	1
Net actuarial loss	56	44
Total net (benefit) expense	(45)	(28)
U.S. | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	0	0
Interest cost on benefit obligation	5	7
Expected return on plan assets	(5)	(5)
Amortization of unrecognized:
Prior service cost (benefit)	0	0
Net actuarial loss	0	0
Total net (benefit) expense	0	2
Non-U.S. plans | Pension Plans
Service-related expense
Benefits earned during the period	37	36
Interest cost on benefit obligation	64	75
Expected return on plan assets	(65)	(68)
Amortization of unrecognized:
Prior service cost (benefit)	(1)	(1)
Net actuarial loss	17	15
Total net (benefit) expense	52	57
Non-U.S. plans | Postretirement Benefit Plans
Service-related expense
Benefits earned during the period	2	2
Interest cost on benefit obligation	24	26
Expected return on plan assets	(20)	(21)
Amortization of unrecognized:
Prior service cost (benefit)	(2)	(2)
Net actuarial loss	5	5
Total net (benefit) expense	$ 9	$ 10