RETIREMENT BENEFITS - Assumptions Used (Details)	1 Months Ended	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Plan Assumptions - At year end
Discount rate (as a percent)	3.20%	3.95%				3.20%								3.95%	3.20%
Expected return on assets (as a percent)	6.80%	6.70%				6.80%				6.80%				6.70%	6.80%	6.80%
VEBA Trust
Plan Assumptions - During the year
Expected return on assets (as a percent)	3.00%													3.00%	3.00%	0.00%
U.S.
Plan Assumptions - During the year
Expected return on assets (as a percent)				6.70%	6.80%
U.S. | Pension Plans | Minimum
Plan Assumptions - During the year
Expected return on assets (as a percent)														6.80%
U.S. | Pension Plans | Maximum
Plan Assumptions - During the year
Expected return on assets (as a percent)														6.70%
U.S. | Postretirement Benefit Plans
Plan Assumptions - At year end
Discount rate (as a percent)	3.50%	4.20%				3.50%								4.20%	3.50%
Expected return on assets (as a percent)	6.80%	6.70%				6.80%								6.70%	6.80%
Plan Assumptions - During the year
Discount rate (as a percent)		4.20%	4.20%	3.90%	3.50%	3.55%	3.60%	3.85%	3.90%	3.30%	3.40%	3.75%	4.20%
Expected return on assets (as a percent)															6.80%	7.00%
U.S. | VEBA Trust
Plan Assumptions - At year end
Expected return on assets (as a percent)	3.00%	3.00%				3.00%								3.00%	3.00%
Non-U.S. | Pension Plans | Weighted Average
Plan Assumptions - At year end
Discount rate (as a percent)	4.17%	4.47%				4.17%								4.47%	4.17%
Future compensation increase rate (as a percent)	3.08%	3.16%				3.08%								3.16%	3.08%
Expected return on assets (as a percent)	4.52%	4.30%				4.52%								4.30%	4.52%
Plan Assumptions - During the year
Discount rate (as a percent)														4.17%	4.40%	4.76%
Future compensation increase rate (as a percent)														3.08%	3.21%	3.24%
Expected return on assets (as a percent)														4.52%	4.55%	4.95%
Non-U.S. | Pension Plans | Minimum
Plan Assumptions - At year end
Discount rate (as a percent)	0.00%	0.25%				0.00%								0.25%	0.00%
Future compensation increase rate (as a percent)	1.17%	1.30%				1.17%								1.30%	1.17%
Expected return on assets (as a percent)	0.00%	1.00%				0.00%								1.00%	0.00%
Plan Assumptions - During the year
Discount rate (as a percent)														0.00%	0.25%	0.25%
Future compensation increase rate (as a percent)														1.17%	1.25%	1.00%
Expected return on assets (as a percent)														1.00%	1.60%	1.30%
Non-U.S. | Pension Plans | Maximum
Plan Assumptions - At year end
Discount rate (as a percent)	10.20%	12.00%				10.20%								12.00%	10.20%
Future compensation increase rate (as a percent)	13.67%	13.67%				13.67%								13.67%	13.67%
Expected return on assets (as a percent)	11.50%	11.50%				11.50%								11.50%	11.50%
Plan Assumptions - During the year
Discount rate (as a percent)														10.75%	72.50%	42.00%
Future compensation increase rate (as a percent)														13.67%	70.00%	40.00%
Expected return on assets (as a percent)														11.50%	11.50%	11.50%
Non-U.S. | Postretirement Benefit Plans | Weighted Average
Plan Assumptions - At year end
Discount rate (as a percent)	8.10%	9.05%				8.10%								9.05%	8.10%
Expected return on assets (as a percent)	8.01%	8.01%				8.01%								8.01%	8.01%
Plan Assumptions - During the year
Discount rate (as a percent)														8.10%	8.27%	7.90%
Expected return on assets (as a percent)														8.01%	8.02%	8.01%
Non-U.S. | Postretirement Benefit Plans | Minimum
Plan Assumptions - At year end
Discount rate (as a percent)	1.75%	1.75%				1.75%								1.75%	1.75%
Expected return on assets (as a percent)	8.00%	8.00%				8.00%								8.00%	8.00%
Plan Assumptions - During the year
Discount rate (as a percent)														1.75%	1.75%	2.00%
Expected return on assets (as a percent)														8.00%	8.00%	8.00%
Non-U.S. | Postretirement Benefit Plans | Maximum
Plan Assumptions - At year end
Discount rate (as a percent)	10.10%	10.75%				10.10%								10.75%	10.10%
Expected return on assets (as a percent)	9.80%	9.20%				9.80%								9.20%	9.80%
Plan Assumptions - During the year
Discount rate (as a percent)														10.10%	11.05%	13.20%
Expected return on assets (as a percent)														9.80%	10.30%	10.70%
Qualified | U.S. | Pension Plans
Plan Assumptions - At year end
Discount rate (as a percent)	3.60%	4.25%				3.60%								4.25%	3.60%
Expected return on assets (as a percent)	680.00%	7.00%				680.00%								7.00%	680.00%
Plan Assumptions - During the year
Discount rate (as a percent)		4.30%	4.25%	3.95%	3.60%	3.75%	3.80%	4.05%	4.10%	3.55%	3.65%	3.95%	4.40%
Expected return on assets (as a percent)															6.80%	7.00%
Nonqualified | U.S. | Pension Plans
Plan Assumptions - At year end
Discount rate (as a percent)	3.60%	4.25%				3.60%								4.25%	3.60%
Plan Assumptions - During the year
Discount rate (as a percent)		4.30%	4.25%	3.95%	3.60%	3.65%	3.75%	3.95%	4.00%	3.45%	3.55%	3.90%	4.35%