RETIREMENT BENEFITS PLANS - Change in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets
Balance at January 1	$ 5,336
Balance at December 31	5,600	$ 5,336
Pension plans
Change in plan assets
Employer contributions	122	119	$ 126
Pension plans | United States
Change in plan assets
Balance at January 1	3,433	3,068
Actual return on plan assets	342	618
Employer contributions	18	17	17
Gross benefits paid	(330)	(270)
Currency translation	0	0
Plan assets reclassified to held for sale	0	0
Other	0	0
Balance at December 31	3,463	3,433	3,068
Pension plans | Foreign Plan
Change in plan assets
Balance at January 1	1,903	1,560
Actual return on plan assets	185	230
Employer contributions	104	102	109
Gross benefits paid	(121)	(102)
Currency translation	69	58
Plan assets reclassified to held for sale	(5)	0
Other	2	55
Balance at December 31	2,137	1,903	1,560
Other postretirement benefits plans
Change in plan assets
Balance at January 1	23	37
Actual return on plan assets	1	5
Employer contributions	23	15
Gross benefits paid	(49)	(60)
Currency translation	0	0
Plan assets reclassified to held for sale	0	0
Other	22	26
Balance at December 31	$ 20	$ 23	$ 37