ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 12,783	$ 26,420	$ 12,466	$ 12,783	$ 12,315
Gross credit losses on loans		(2,367)	(2,281)	(7,374)	(6,980)
Gross recoveries on loans		448	368	1,141	1,156
Net credit losses on loans (NCLs)		(1,919)	(1,913)	(6,233)	(5,824)
Net reserve builds (releases) for loans		42	132	9,010	252
Net specific reserve builds (releases) for loans		(152)	17	706	19
Total provision for credit losses on loans (PCLL)		1,809	2,062	15,949	6,095
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other, net		116	(85)	(278)	(56)
ACLL at end of period		26,426	12,530	26,426	12,530
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	1,456	1,859	1,376	1,456	1,367
Provision (release) for credit losses on unfunded lending commitments		424	9	1,094	18
Other, net		16	0	(57)	0
ACLUC at end of period		2,299	1,385	2,299	1,385
Total allowance for credit losses on loans, leases and unfunded lending commitments		28,725	13,915	28,725	13,915
Sales or transfers of various consumer loan portfolios to HFS
Sales or transfers of various consumer loan portfolios to HFS		0	(5)	(4)	(9)
FX translation		116	(65)	(279)	(26)
Other		0	(15)	5	(21)
Other liabilities		58,003		58,003			$ 57,979
Revision of Prior Period, Change in Accounting Principle, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period		(426)
ACLL at end of period		(122)		(122)
Revision of Prior Period, Reclassification, Adjustment
Allowance for credit losses
Gross recoveries on loans		(50)
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period		(68)
Sales or transfers of various consumer loan portfolios to HFS
Other liabilities						$ 68
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	4,201	0		4,201	0
Net reserve builds (releases) for loans	4,900
ACLL at end of period	4,100
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	(194)	0		(194)
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	16,984	26,420		16,984
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	2,886	6,824	2,787	2,886	2,811
Gross credit losses on loans		(351)	(129)	(836)	(333)
Gross recoveries on loans		26	19	60	55
Net credit losses on loans (NCLs)		(325)	(110)	(776)	(278)
Net reserve builds (releases) for loans		267	37	4,418	91
Net specific reserve builds (releases) for loans		(161)	(1)	373	(77)
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	0	0
Other, net		8	(20)	(18)	(22)
ACLL at end of period		6,938	2,803	6,938	2,803
Corporate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	(721)			(721)	0
Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	9,897	19,596	9,679	9,897	9,504
Gross credit losses on loans		(2,016)	(2,152)	(6,538)	(6,647)
Gross recoveries on loans		422	349	1,081	1,101
Net credit losses on loans (NCLs)		(1,594)	(1,803)	(5,457)	(5,546)
Net reserve builds (releases) for loans		(225)	95	4,592	161
Net specific reserve builds (releases) for loans		9	18	333	96
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other, net		108	(65)	(260)	(34)
ACLL at end of period		$ 19,488	$ 9,727	19,488	9,727
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 4,922			$ 4,922	$ 0