CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Change in accumulated other comprehensive income (loss)
Balance, beginning of period			$ 200,200
Balance, end of period	$ 201,610	$ 194,595	201,610	$ 194,595
Discontinued Operations, Held-for-sale | Australia Consumer Banking Business
Change in accumulated other comprehensive income (loss)
Loss on sale of business, foreign currency translation adjustments, after-tax	475		475
Pretax loss on sale of business	680		680
Loss on sale of business, after-tax	580		580
Loss on sale of business, foreign currency translation adjustments	625		625
Net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	1,061	3,700	3,320	(265)
Other comprehensive income before reclassifications	(204)	(72)	(2,101)	4,735
Increase (decrease) due to amounts reclassified from AOCI	(75)	(210)	(437)	(1,052)
Total other comprehensive income	(279)	(282)	(2,538)	3,683
Balance, end of period	782	3,418	782	3,418
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(1,523)	(36)	(1,419)	(944)
Other comprehensive income before reclassifications	(138)	(313)	(295)	599
Increase (decrease) due to amounts reclassified from AOCI	56	6	109	2
Total other comprehensive income	(82)	(307)	(186)	601
Balance, end of period	(1,605)	(343)	(1,605)	(343)
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	864	2,094	1,593	123
Other comprehensive income before reclassifications	2	(41)	(318)	2,083
Increase (decrease) due to amounts reclassified from AOCI	(203)	(194)	(612)	(347)
Total other comprehensive income	(201)	(235)	(930)	1,736
Balance, end of period	663	1,859	663	1,859
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(6,063)	(7,172)	(6,864)	(6,809)
Other comprehensive income before reclassifications	84	189	773	(287)
Increase (decrease) due to amounts reclassified from AOCI	51	57	163	170
Total other comprehensive income	135	246	936	(117)
Balance, end of period	(5,928)	(6,926)	(5,928)	(6,926)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(29,392)	(31,939)	(28,641)	(28,391)
Other comprehensive income before reclassifications	(1,325)	897	(2,076)	(2,651)
Increase (decrease) due to amounts reclassified from AOCI	13	0	13	0
Total other comprehensive income	(1,312)	897	(2,063)	(2,651)
Balance, end of period	(30,704)	(31,042)	(30,704)	(31,042)
Excluded component of fair value hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(67)	8	(47)	(32)
Other comprehensive income before reclassifications	7	(39)	(14)	1
Increase (decrease) due to amounts reclassified from AOCI	1	0	2	0
Total other comprehensive income	8	(39)	(12)	1
Balance, end of period	(59)	(31)	(59)	(31)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(35,120)	(33,345)	(32,058)	(36,318)
Other comprehensive income before reclassifications	(1,574)	621	(4,031)	4,480
Increase (decrease) due to amounts reclassified from AOCI	(157)	(341)	(762)	(1,227)
Total other comprehensive income	(1,731)	280	(4,793)	3,253
Balance, end of period	$ (36,851)	$ (33,065)	$ (36,851)	$ (33,065)