RETIREMENT BENEFITS - Level 3 Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
U.S. | Non-U.S. equities
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	$ 821
Plan assets at fair value at end of period	481	$ 821
U.S. | Non-U.S. equities | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	0
Plan assets at fair value at end of period	0	0
U.S. | Debt securities
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	4,461
Plan assets at fair value at end of period	4,821	4,461
U.S. | Debt securities | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	0
Plan assets at fair value at end of period	0	0
U.S. | Annuity contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	1
Plan assets at fair value at end of period	1	1
U.S. | Annuity contracts | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	1	1
Realized gains (losses)	0	0
Unrealized gains (losses)	0	0
Purchases, sales, and issuances	0	0
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	1	1
U.S. | Other investments
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	148
Plan assets at fair value at end of period	127	148
U.S. | Other investments | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	148	129
Realized gains (losses)	(2)	0
Unrealized gains (losses)	(18)	0
Purchases, sales, and issuances	(1)	19
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	127	148
U.S. | Total investments
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	8,051
Plan assets at fair value at end of period	7,882	8,051
U.S. | Total investments | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	149	130
Realized gains (losses)	(2)	0
Unrealized gains (losses)	(18)	0
Purchases, sales, and issuances	(1)	19
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	128	149
Non-U.S. | Non-U.S. equities
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	226
Plan assets at fair value at end of period	200	226
Non-U.S. | Non-U.S. equities | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	1	1
Unrealized gains (losses)	0	0
Purchases, sales, and issuances	0	0
Transfers in and/or out of Level 3	(1)	0
Plan assets at fair value at end of period	0	1
Non-U.S. | Debt securities
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	5,561
Plan assets at fair value at end of period	6,654	5,561
Non-U.S. | Debt securities | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	7	7
Unrealized gains (losses)	(1)	0
Purchases, sales, and issuances	3	0
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	9	7
Non-U.S. | Real estate
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	4
Plan assets at fair value at end of period	4	4
Non-U.S. | Real estate | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	1	1
Unrealized gains (losses)	0	0
Purchases, sales, and issuances	0	0
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	1	1
Non-U.S. | Annuity contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	10
Plan assets at fair value at end of period	11	10
Non-U.S. | Annuity contracts | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	9	8
Unrealized gains (losses)	(1)	1
Purchases, sales, and issuances	1	0
Transfers in and/or out of Level 3	1	0
Plan assets at fair value at end of period	10	9
Non-U.S. | Other investments
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	215
Plan assets at fair value at end of period	211	215
Non-U.S. | Other investments | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	214	187
Unrealized gains (losses)	(3)	31
Purchases, sales, and issuances	(1)	(4)
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	210	214
Non-U.S. | Total investments
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	12,331
Plan assets at fair value at end of period	10,220	12,331
Non-U.S. | Total investments | Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Plan assets at fair value at beginning of period	232	204
Unrealized gains (losses)	(5)	32
Purchases, sales, and issuances	3	(4)
Transfers in and/or out of Level 3	0	0
Plan assets at fair value at end of period	$ 230	$ 232