ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 12,783	$ 12,315
Gross credit losses on loans	(2,479)	(2,345)
Gross recoveries	371	397
Net credit losses on loans (NCLs)	(2,108)	(1,948)
Net reserve builds (releases) for loans	4,112	67
Net specific reserve builds (releases) for loans	224	(71)
Total provision for credit losses on loans (PCLL)	6,444	1,944
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period	4	0
Other, net	(483)	18
ACLL at end of period	20,841	12,329
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	1,456	1,367
Provision (release) for credit losses on unfunded lending commitments	557	24
Other, net	(6)	0
ACLUC at end of period	1,813	1,391
Total allowance for credit losses on loans, leases and unfunded lending commitments	22,654	13,720
Sales or transfers of various consumer loan portfolios to HFS
Sales or transfers of various consumer loan portfolios to HFS	(3)	0
FX translation	(483)	26
Other	3	(8)
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	4,201
Allowance for credit losses on unfunded commitments
Allowance for credit losses on unfunded commitments (ACLUC) at beginning of period	(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
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	2,886	2,811
Gross credit losses on loans	(138)	(100)
Gross recoveries	11	21
Net credit losses on loans (NCLs)	(127)	(79)
Net reserve builds (releases) for loans	1,268	4
Net specific reserve builds (releases) for loans	48	(79)
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period	0	0
Other, net	(30)	(5)
ACLL at end of period	3,451	2,731
Corporate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	(721)
Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	9,897	9,504
Gross credit losses on loans	(2,341)	(2,245)
Gross recoveries	360	376
Net credit losses on loans (NCLs)	(1,981)	(1,869)
Net reserve builds (releases) for loans	2,844	63
Net specific reserve builds (releases) for loans	176	8
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period	4	0
Other, net	(453)	23
ACLL at end of period	17,390	$ 9,598
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 4,922