ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	$ 12,783	$ 12,783	$ 12,315	$ 12,355
Charge-offs		(9,263)	(9,341)	(8,665)
Recoveries		1,652	1,573	1,552
Replenishment of net charge-offs		7,611	7,768	7,113
Net reserve builds (releases)		7,635	364	394
Net specific reserve builds (releases)		676	86	(153)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		4	0	0
Other		100	18	(281)
ACLL at end of year		24,956	12,783	12,315
Allowance for credit losses on loans
Collectively evaluated					$ 23,094	$ 11,293
Individually evaluated					1,860	1,489
Total allowance for credit losses on loans	12,783	24,956	12,315	12,355	24,956	12,783
Loans, net of unearned income
Collectively evaluated					660,562	688,622
Individually evaluated					8,326	6,648
Loans at fair value					6,854	4,085
Loans, net of unearned income					675,883	699,483
Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated					2	1
Loans, net of unearned income
Purchased credit deteriorated					141	128
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	2,886	2,886	2,811	2,943
Charge-offs		(1,072)	(487)	(343)
Recoveries		86	95	138
Replenishment of net charge-offs		986	392	205
Net reserve builds (releases)		2,890	96	42
Net specific reserve builds (releases)		282	(21)	(151)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0
Other		65	0	(23)
ACLL at end of year		5,402	2,886	2,811
Allowance for credit losses on loans
Collectively evaluated					4,887	2,587
Individually evaluated					515	299
Total allowance for credit losses on loans	2,886	2,886	2,811	2,811	5,402	2,886
Loans, net of unearned income
Collectively evaluated					376,677	383,828
Individually evaluated					3,527	2,040
Loans at fair value					6,840	4,067
Loans, net of unearned income					387,044	389,935
Corporate | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated					0	0
Loans, net of unearned income
Purchased credit deteriorated					0	0
Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	9,897	9,897	9,504	9,412
Charge-offs		(8,191)	(8,854)	(8,322)
Recoveries		1,566	1,478	1,414
Replenishment of net charge-offs		6,625	7,376	6,908
Net reserve builds (releases)		4,745	268	352
Net specific reserve builds (releases)		394	107	(2)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		4
Other		35	18	(258)
ACLL at end of year		19,554	9,897	9,504
Allowance for credit losses on loans
Collectively evaluated					18,207	8,706
Individually evaluated					1,345	1,190
Total allowance for credit losses on loans	9,897	19,554	9,504	9,412	19,554	9,897
Loans, net of unearned income
Collectively evaluated					283,885	304,794
Individually evaluated					4,799	4,608
Loans at fair value					14	18
Loans, net of unearned income					288,839	309,548
Consumer | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated					2	1
Loans, net of unearned income
Purchased credit deteriorated					$ 141	128
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
Net reserve builds (releases)	4,900
ACLL at end of year	4,100		4,201
Allowance for credit losses on loans
Total allowance for credit losses on loans	4,201	4,201	4,201			4,201
Cumulative Effect, Period of Adoption, Adjustment | Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	0	0
ACLL at end of year			0
Allowance for credit losses on loans
Total allowance for credit losses on loans	0	0	0			0
Cumulative Effect, Period of Adoption, Adjustment | Corporate | Accounting Standards Update 2016-13
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	(721)	(721)
ACLL at end of year			(721)
Allowance for credit losses on loans
Total allowance for credit losses on loans	(721)	(721)	(721)			(721)
Cumulative Effect, Period of Adoption, Adjustment | Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	(443)	(443)
ACLL at end of year			(443)
Allowance for credit losses on loans
Total allowance for credit losses on loans	(443)	(443)	(443)			(443)
Cumulative Effect, Period of Adoption, Adjustment | Consumer | Accounting Standards Update 2016-13
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	4,922	4,922
ACLL at end of year			4,922
Allowance for credit losses on loans
Total allowance for credit losses on loans	4,922	4,922	4,922			4,922
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	12,315	12,355
ACLL at end of year			16,541	12,315
Allowance for credit losses on loans
Total allowance for credit losses on loans	16,541	16,541	12,315	$ 12,355		16,541
Cumulative Effect, Period of Adoption, Adjusted Balance | Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	2,165	2,165
ACLL at end of year			2,165
Allowance for credit losses on loans
Total allowance for credit losses on loans	2,165	2,165	2,165			2,165
Cumulative Effect, Period of Adoption, Adjusted Balance | Consumer
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	14,376	14,376
ACLL at end of year			14,376
Allowance for credit losses on loans
Total allowance for credit losses on loans	$ 14,376	$ 14,376	$ 14,376			$ 14,376