RETIREMENT BENEFITS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		$ 202,672
Change, net of tax	[1]	171	$ 714
Balance, end of period		198,353	203,273	$ 202,672
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(5,852)	(6,864)	(6,864)
Actuarial assumptions changes and plan experience		1,525	1,430	963
Net asset loss due to difference between actual and expected returns		(1,462)	(718)	(148)
Net amortization		64	81	280
Prior service cost		0	0	(7)
Curtailment/settlement gain		0	0	11
Foreign exchange impact and other		50	114	153
Change in deferred taxes, net		(6)	(193)	(240)
Change, net of tax		171	714	1,012
Balance, end of period		$ (5,681)	$ (6,150)	$ (5,852)

[1] See Note 17.