RETIREMENT BENEFITS - Net (Benefit) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure
Percentage of the significant plans over global pension and postretirement liabilities, which utilize quarterly measurement policy	90.00%
Defined Benefit Plan, Net Periodic Benefit Cost
Interest cost on benefit obligation	$ 2	$ 2	$ 3
Expected return on plan assets	(1)	0	0
Amortization of unrecognized
Prior service cost (benefit)	(23)	(31)	(31)
Total net expense	(18)	3	(2)
U.S. | Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost
Benefits earned during the year	1	3	4
Interest cost on benefit obligation	514	533	548
Expected return on plan assets	(844)	(865)	(886)
Amortization of unrecognized
Prior service cost (benefit)	2	2	2
Net actuarial loss (gain)	165	173	169
Curtailment loss (gain)	1	6	13
Settlement loss	0	0	0
Total net expense	(161)	(148)	(150)
U.S. | Postretirement Benefit Plans
Defined Benefit Plan, Net Periodic Benefit Cost
Benefits earned during the year	0	0	0
Interest cost on benefit obligation	26	26	25
Expected return on plan assets	(14)	(6)	(9)
Amortization of unrecognized
Prior service cost (benefit)	0	0	0
Net actuarial loss (gain)	(1)	0	(1)
Curtailment loss (gain)	0	0	0
Settlement loss	0	0	0
Total net expense	11	20	15
Non-U.S. | Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost
Benefits earned during the year	146	153	154
Interest cost on benefit obligation	292	295	282
Expected return on plan assets	(291)	(299)	(287)
Amortization of unrecognized
Prior service cost (benefit)	(4)	(3)	(1)
Net actuarial loss (gain)	53	61	69
Curtailment loss (gain)	(1)	0	(2)
Settlement loss	7	12	6
Total net expense	202	219	221
Non-U.S. | Postretirement Benefit Plans
Defined Benefit Plan, Net Periodic Benefit Cost
Benefits earned during the year	9	9	10
Interest cost on benefit obligation	102	101	94
Expected return on plan assets	(88)	(89)	(86)
Amortization of unrecognized
Prior service cost (benefit)	(10)	(10)	(10)
Net actuarial loss (gain)	29	35	30
Curtailment loss (gain)	0	0	0
Settlement loss	0	0	0
Total net expense	$ 42	$ 46	$ 38