ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 12,783	$ 20,841	$ 12,329	$ 12,783	$ 12,315
Gross credit losses on loans		(2,528)	(2,354)	(5,007)	(4,699)
Gross recoveries on loans		322	391	693	788
Net credit losses on loans (NCLs)		(2,206)	(1,963)	(4,314)	(3,911)
Net reserve builds (releases)		4,856	53	8,968	120
Net specific reserve builds (releases) for loans		634	73	858	2
Total provision for credit losses on loans (PCLL)		7,696	2,089	14,140	4,033
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other, net		89	11	(394)	29
ACLL at end of period		26,420	12,466	26,420	12,466
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	1,456	1,813	1,391	1,456	1,367
Provision (release) for credit losses on unfunded lending commitments		113	(15)	670	9
Other, net		(67)	0	(73)	0
ACLUC at end of period		1,859	1,376	1,859	1,376
Total allowance for credit losses on loans, leases and unfunded lending commitments		28,279	13,842	28,279	13,842
Sales or transfers of various consumer loan portfolios to HFS
Sales or transfers of various consumer loan portfolios to HFS		(1)	(4)	(4)	(4)
FX translation		88	13	(395)	39
Other		2	2	5	(6)
Other liabilities		61,269		61,269		$ 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
ACLL at end of period		(426)		(426)
Revision of Prior Period, Reclassification, Adjustment
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period
ACLUC at end of period		(68)		(68)
Sales or transfers of various consumer loan portfolios to HFS
Other liabilities		68		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)	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	20,841		16,984
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	2,886	3,451	2,731	2,886	2,811
Gross credit losses on loans		(347)	(104)	(485)	(204)
Gross recoveries on loans		23	15	34	36
Net credit losses on loans (NCLs)		(324)	(89)	(451)	(168)
Net reserve builds (releases)		2,883	50	4,151	54
Net specific reserve builds (releases) for loans		486	3	534	(76)
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	0	0
Other, net		4	3	(26)	(2)
ACLL at end of period		6,824	2,787	6,824	2,787
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	17,390	9,598	9,897	9,504
Gross credit losses on loans		(2,181)	(2,250)	(4,522)	(4,495)
Gross recoveries on loans		299	376	659	752
Net credit losses on loans (NCLs)		(1,882)	(1,874)	(3,863)	(3,743)
Net reserve builds (releases)		1,973	3	4,817	66
Net specific reserve builds (releases) for loans		148	70	324	78
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other, net		85	8	(368)	31
ACLL at end of period		$ 19,596	$ 9,679	19,596	9,679
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