ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Jun. 30, 2020
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	$ 12,783	$ 24,956	$ 12,783	$ 12,315
Gross credit losses on loans		(6,720)	(9,263)	(9,341)
Gross recoveries on loans		1,825	1,652	1,573
Replenishment of net charge-offs		4,895	7,611	7,768
Net reserve builds (releases)		(7,283)	7,635	364
Net specific reserve builds (releases)		(715)	676	86
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	4	0
Other		(503)	100	18
ACLL at end of year		16,455	24,956	12,783
Allowance for credit losses on loans
Collectively evaluated		15,430	23,094
Individually evaluated		1,025	1,860
Total allowance for credit losses on loans		16,455	24,956	12,783
Loans, net of unearned income
Collectively evaluated		656,008	660,562
Individually evaluated		5,558	8,326
Loans held at fair value		6,082	6,854
Total		667,767	675,883
Variable post-charge-off third-party collection costs
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	(443)		(443)
ACLL at end of year	(443)			(443)
Allowance for credit losses on loans
Total allowance for credit losses on loans	(443)			(443)	$ (122)	$ (426)
Purchased credit deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		0	2
Loans, net of unearned income
Purchased credit deteriorated		119	141
Corporate
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	2,886	5,402	2,886	2,811
Gross credit losses on loans		(522)	(1,072)	(487)
Gross recoveries on loans		127	86	95
Replenishment of net charge-offs		395	986	392
Net reserve builds (releases)		(2,254)	2,890	96
Net specific reserve builds (releases)		(278)	282	(21)
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	0
Other		(31)	65	0
ACLL at end of year		2,839	5,402	2,886
Allowance for credit losses on loans
Collectively evaluated		2,614	4,887
Individually evaluated		225	515
Total allowance for credit losses on loans		2,839	5,402	2,886
Loans, net of unearned income
Collectively evaluated		388,584	376,677
Individually evaluated		1,877	3,527
Loans held at fair value		6,070	6,840
Total		396,531	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 year	0		0
ACLL at end of year				0
Allowance for credit losses on loans
Total allowance for credit losses on loans				0
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	19,554	9,897	9,504
Gross credit losses on loans		(6,198)	(8,191)	(8,854)
Gross recoveries on loans		1,698	1,566	1,478
Replenishment of net charge-offs		4,500	6,625	7,376
Net reserve builds (releases)		(5,029)	4,745	268
Net specific reserve builds (releases)		(437)	394	107
Initial allowance for credit losses on newly purchased credit-deteriorated assets during the period		0	4
Other		(472)	35	18
ACLL at end of year		13,616	19,554	9,897
Allowance for credit losses on loans
Collectively evaluated		12,816	18,207
Individually evaluated		800	1,345
Total allowance for credit losses on loans		13,616	19,554	9,897
Loans, net of unearned income
Collectively evaluated		267,424	283,885
Individually evaluated		3,681	4,799
Loans held at fair value		12	14
Total		271,236	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 year	(443)		(443)
ACLL at end of year				(443)
Allowance for credit losses on loans
Total allowance for credit losses on loans				(443)
Consumer | Purchased credit deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		0	2
Loans, net of unearned income
Purchased credit deteriorated		$ 119	141
Adjustment to opening balance for CECL adoption
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	4,100			4,201
Adjustment to opening balance for CECL adoption | Corporate
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)
Adjustment to opening balance for CECL adoption | Consumer
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
Adjusted balance
Allowance for credit losses
Allowance for credit losses on loans (ACLL) at beginning of year	16,541		16,541
ACLL at end of year				16,541
Allowance for credit losses on loans
Total allowance for credit losses on loans				16,541
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
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