ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses Roll Forward (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	$ 12,783			$ 12,783	$ 12,783	$ 12,315	$ 12,355
Gross credit losses on loans					(9,263)	(9,341)	(8,665)
Gross recoveries on loans					1,652	1,573	1,552
Net credit losses on loans (NCLs)					(7,611)	(7,768)	(7,113)
Net reserve builds (releases)					7,635	364	394
Net specific reserve builds (releases) for loans					676	86	(153)
Total provision for credit losses on loans (PCLL)					15,922	8,218	7,354
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period					4	0	0
Other, net					100	18	(281)
ACLL at end of year					24,956	12,783	12,315
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	1,456			1,456	1,456	1,367	1,258
Provision (release) for credit losses on unfunded lending commitments					1,446	92	113
Other, net					(53)	(3)	(4)
ACLUC at end of period					2,655	1,456	1,367
Total allowance for credit losses on loans, leases and unfunded lending commitments					27,611	14,239	13,682
Sales or transfers of various consumer loan portfolios to held-for-sale
Other liabilities, at fair value					59,983	57,979
Previously Reported
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	12,783			12,783	12,783
ACLL at end of year						12,783
Revision of Prior Period, Change in Accounting Principle, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	(443)	$ (426)		(443)	(443)
Total provision for credit losses on loans (PCLL)		122	$ 339	(18)
ACLL at end of year	(443)	$ (122)	$ (426)			(443)
Revision of Prior Period, Reclassification, Adjustment
Allowance for credit losses on unfunded commitments
ACLUC at end of period					(68)
Sales or transfers of various consumer loan portfolios to held-for-sale
Other liabilities, at fair value					68
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	4,201			4,201	4,201
Net reserve builds (releases)	4,900
ACLL at end of year	4,100					4,201
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	(194)			(194)	(194)
ACLUC at end of period						(194)
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	16,541			16,541	16,541	12,315	12,355
ACLL at end of year						16,541	12,315
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	2,886			2,886	2,886	2,811	2,943
Gross credit losses on loans					(1,072)	(487)	(343)
Gross recoveries on loans					86	95	138
Net credit losses on loans (NCLs)					(986)	(392)	(205)
Net reserve builds (releases)					2,890	96	42
Net specific reserve builds (releases) for loans					282	(21)	(151)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period					0
Other, net					65	0	(23)
ACLL at end of year					5,402	2,886	2,811
Sales or transfers of various consumer loan portfolios to held-for-sale
FX translation					97	60	(60)
Other					7	0	(20)
Corporate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	0			0	0
ACLL at end of year						0
Corporate | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	2,165			2,165	2,165
ACLL at end of year						2,165
Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	9,897			9,897	9,897	9,504	9,412
Gross credit losses on loans					(8,191)	(8,854)	(8,322)
Gross recoveries on loans					1,566	1,478	1,414
Net credit losses on loans (NCLs)					(6,625)	(7,376)	(6,908)
Net reserve builds (releases)					4,745	268	352
Net specific reserve builds (releases) for loans					394	107	(2)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period					4
Other, net					35	18	(258)
ACLL at end of year					19,554	9,897	9,504
Sales or transfers of various consumer loan portfolios to held-for-sale
Transfer of real estate loan portfolios					4	42	91
Transfer of other loan portfolios					0	0	110
Sales or transfers of various consumer loan portfolios to HFS					(4)	(42)	$ (201)
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	(443)			(443)	(443)
ACLL at end of year						(443)
Consumer | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	$ 14,376			$ 14,376	$ 14,376
ACLL at end of year						$ 14,376