RETIREMENT BENEFITS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Change in accumulated other comprehensive income (loss)
Balance, beginning of period				$ 193,946
Actuarial assumptions changes and plan experience		$ (26)		(826)
Net asset gain due to difference between actual and expected returns		271		249
Net amortization		81		229
Prior service cost		104		120
Curtailment/settlement gain		(5)		(2)
Foreign exchange impact and other		(80)		64
Change in deferred taxes, net		(99)		49
Change, net of tax	[1]	246	$ (250)	(117)	$ (567)
Balance, end of period		194,595	197,070	194,595	197,070
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(7,172)	(6,574)	(6,809)	(6,257)
Balance, end of period		$ (6,926)	$ (6,824)	$ (6,926)	$ (6,824)

[1] See Note 17 to the Consolidated Financial Statements.