CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	$ 200,200
Balance, end of period	203,273	$ 193,326
Net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	3,320	(265)
Other comprehensive income before reclassifications	(1,519)	3,417
Increase (decrease) due to amounts reclassified from AOCI	(266)	(289)
Total other comprehensive income	(1,785)	3,128
Balance, end of period	1,535	2,863
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(1,419)	(944)
Other comprehensive income before reclassifications	(84)	3,116
Increase (decrease) due to amounts reclassified from AOCI	42	24
Total other comprehensive income	(42)	3,140
Balance, end of period	(1,461)	2,196
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	1,593	123
Other comprehensive income before reclassifications	(344)	1,898
Increase (decrease) due to amounts reclassified from AOCI	(212)	(1)
Total other comprehensive income	(556)	1,897
Balance, end of period	1,037	2,020
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(6,864)	(6,809)
Other comprehensive income before reclassifications	653	(344)
Increase (decrease) due to amounts reclassified from AOCI	61	58
Total other comprehensive income	714	(286)
Balance, end of period	(6,150)	(7,095)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(28,641)	(28,391)
Other comprehensive income before reclassifications	(1,274)	(4,109)
Increase (decrease) due to amounts reclassified from AOCI	0	0
Total other comprehensive income	(1,274)	(4,109)
Balance, end of period	(29,915)	(32,500)
Excluded component of fair value hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(47)	(32)
Other comprehensive income before reclassifications	(10)	27
Increase (decrease) due to amounts reclassified from AOCI	0	0
Total other comprehensive income	(10)	27
Balance, end of period	(57)	(5)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(32,058)	(36,318)
Other comprehensive income before reclassifications	(2,578)	4,005
Increase (decrease) due to amounts reclassified from AOCI	(375)	(208)
Total other comprehensive income	(2,953)	3,797
Balance, end of period	$ (35,011)	$ (32,521)