CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (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
Balance, end of period	$ 202,910	$ 192,386	202,910	$ 192,386
Net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	1,535	2,863	3,320	(265)
Other comprehensive income before reclassifications	(379)	1,391	(1,898)	4,795
Increase (decrease) due to amounts reclassified from AOCI	(95)	(554)	(361)	(830)
Total other comprehensive income	(474)	837	(2,259)	3,965
Balance, end of period	1,061	3,700	1,061	3,700
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(1,461)	2,196	(1,419)	(944)
Other comprehensive income before reclassifications	(72)	(2,204)	(156)	913
Increase (decrease) due to amounts reclassified from AOCI	10	(28)	52	(5)
Total other comprehensive income	(62)	(2,232)	(104)	908
Balance, end of period	(1,523)	(36)	(1,523)	(36)
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	1,037	2,020	1,593	123
Other comprehensive income before reclassifications	28	226	(316)	2,124
Increase (decrease) due to amounts reclassified from AOCI	(201)	(152)	(413)	(153)
Total other comprehensive income	(173)	74	(729)	1,971
Balance, end of period	864	2,094	864	2,094
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(6,150)	(7,095)	(6,864)	(6,809)
Other comprehensive income before reclassifications	36	(132)	689	(476)
Increase (decrease) due to amounts reclassified from AOCI	51	55	112	113
Total other comprehensive income	87	(77)	801	(363)
Balance, end of period	(6,063)	(7,172)	(6,063)	(7,172)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(29,915)	(32,500)	(28,641)	(28,391)
Other comprehensive income before reclassifications	523	561	(751)	(3,548)
Increase (decrease) due to amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income	523	561	(751)	(3,548)
Balance, end of period	(29,392)	(31,939)	(29,392)	(31,939)
Excluded component of fair value hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(57)	(5)	(47)	(32)
Other comprehensive income before reclassifications	(11)	13	(21)	40
Increase (decrease) due to amounts reclassified from AOCI	1	0	1	0
Total other comprehensive income	(10)	13	(20)	40
Balance, end of period	(67)	8	(67)	8
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(35,011)	(32,521)	(32,058)	(36,318)
Other comprehensive income before reclassifications	125	(145)	(2,453)	3,848
Increase (decrease) due to amounts reclassified from AOCI	(234)	(679)	(609)	(875)
Total other comprehensive income	(109)	(824)	(3,062)	2,973
Balance, end of period	$ (35,120)	$ (33,345)	$ (35,120)	$ (33,345)