ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 12,783	$ 21,638	$ 20,380	$ 24,956	$ 12,783
Charge-offs		(1,844)	(2,528)	(4,052)	(5,007)
Recoveries		524	367	984	787
Replenishment of NCLs		1,320	2,161	3,068	4,220
Net reserve builds (releases)		(2,184)	5,195	(5,252)	9,289
Net specific reserve builds (releases)		(262)	634	(421)	858
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	0	0	4
Other		46	89	(45)	(394)
ACLL at end of period		19,238	26,298	19,238	26,298
ACLL
Collectively evaluated		17,810		17,810		$ 23,094
Individually evaluated		1,429		1,429		1,860
Total ACLL		19,238	26,298	19,238	26,298	24,956
Loans, net of unearned income
Collectively evaluated		661,948		661,948		660,562
Individually evaluated		7,045		7,045		8,326
Loans held at fair value		7,707		7,707		6,854
Total loans, net of unearned income		676,834		676,834		675,883
Variable post-charge-off third-party collection costs
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	(443)	0	0	0	(443)
ACLL at end of period	(443)
ACLL
Total ACLL	(443)					0
Purchased credit deteriorated(1)
ACLL
Purchased credit deteriorated(1)		(1)		(1)		2
Loans, net of unearned income
Purchased credit deteriorated		134		134		141
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	2,886	4,084	3,451	5,402	2,886
Charge-offs		(151)	(347)	(354)	(485)
Recoveries		62	23	79	34
Replenishment of NCLs		89	324	275	451
Net reserve builds (releases)		(820)	2,883	(2,093)	4,151
Net specific reserve builds (releases)		(130)	486	(168)	534
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	0	0	0
Other		(7)	4	(14)	(26)
ACLL at end of period		3,127	6,824	3,127	6,824
ACLL
Collectively evaluated		2,782		2,782		4,887
Individually evaluated		345		345		515
Total ACLL		3,127	6,824	3,127	6,824	5,402
Loans, net of unearned income
Collectively evaluated		390,670		390,670		376,677
Individually evaluated		2,576		2,576		3,527
Loans held at fair value		7,693		7,693		6,840
Total loans, net of unearned income		400,939		400,939		387,044
Corporate | Variable post-charge-off third-party collection costs
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	0			0	0
ACLL
Total ACLL						0
Corporate | Purchased credit deteriorated(1)
ACLL
Purchased credit deteriorated(1)		0		0		0
Loans, net of unearned income
Purchased credit deteriorated		0		0		0
Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	9,897	17,554	16,929	19,554	9,897
Charge-offs		(1,693)	(2,181)	(3,698)	(4,522)
Recoveries		462	344	905	753
Replenishment of NCLs		1,231	1,837	2,793	3,769
Net reserve builds (releases)		(1,364)	2,312	(3,159)	5,138
Net specific reserve builds (releases)		(132)	148	(253)	324
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	0	0	4
Other		53	85	(31)	(368)
ACLL at end of period		16,111	19,474	16,111	19,474
ACLL
Collectively evaluated		15,028		15,028		18,207
Individually evaluated		1,084		1,084		1,345
Total ACLL		16,111	19,474	16,111	19,474	19,554
Loans, net of unearned income
Collectively evaluated		271,278		271,278		283,885
Individually evaluated		4,469		4,469		4,799
Loans held at fair value		14		14		14
Total loans, net of unearned income		275,895		275,895		288,839
Consumer | Variable post-charge-off third-party collection costs
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	(443)			0	(443)
ACLL
Total ACLL						0
Consumer | Purchased credit deteriorated(1)
ACLL
Purchased credit deteriorated(1)		(1)		(1)		2
Loans, net of unearned income
Purchased credit deteriorated		134		134		141
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	4,201	$ 0	$ 0	0	4,201
Net reserve builds (releases)	4,900
ACLL at end of period	4,100
ACLL
Total ACLL	4,100					0
Cumulative Effect, Period of Adoption, Adjustment | Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	(721)			0	(721)
ACLL
Total ACLL						0
Cumulative Effect, Period of Adoption, Adjustment | Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of period	$ 4,922			$ 0	$ 4,922
ACLL
Total ACLL						$ 0