RETIREMENT BENEFITS - Contributions (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
U.S. | Pension Plans
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]
Company contributions for the nine months ended September 30	$ 15	$ 42	$ 90
Company contributions expected to be made during the remainder of the year		15
U.S. | Postretirement Benefit Plans
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]
Company contributions for the nine months ended September 30	146	159	30
Company contributions expected to be made during the remainder of the year		2
Non-U.S. plans | Pension Plans
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]
Company contributions for the nine months ended September 30	26	143	109
Company contributions expected to be made during the remainder of the year		33
Non-U.S. plans | Postretirement Benefit Plans
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]
Company contributions for the nine months ended September 30	$ 3	7	$ 7
Company contributions expected to be made during the remainder of the year		$ 2