RETIREMENT BENEFITS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Change in accumulated other comprehensive income (loss)
Balance, beginning of period				$ 200,200
Change, net of tax	[1]	$ 87	$ (77)	801	$ (363)
Balance, end of period		202,910	192,386	202,910	192,386
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(6,150)	(7,095)	(6,864)	(6,809)
Actuarial assumptions changes and plan experience		(480)		950
Net asset gain (loss) due to difference between actual and expected returns		509		(209)
Net amortization		66		147
Curtailment/settlement gain		(4)		(4)
Foreign exchange impact and other		(7)		107
Change in deferred taxes, net		3		(190)
Change, net of tax		87		801
Balance, end of period		$ (6,063)	$ (7,172)	$ (6,063)	$ (7,172)

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