ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Allowance for credit losses
Charge-offs		$ (2,208)	$ (2,479)
Recoveries		460	420
Replenishment of net charge-offs		1,748	2,059
Net reserve builds (releases) for loans		(3,068)	4,094
Net specific reserve builds (releases)		(159)	224
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	4
Other		(91)	(483)
Allowance for credit losses on loans
Collectively evaluated		19,934		$ 23,094
Individually evaluated		1,703		1,860
Total allowance for credit losses on loans		21,638	20,380	24,956	$ 12,783
Loans, net of unearned income
Collectively evaluated		650,489		660,562
Individually evaluated		7,839		8,326
Loans at fair value		7,525		6,854
Loans, net of unearned income		665,988		675,883
Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		1		2
Loans, net of unearned income
Purchased credit deteriorated		135		141
Corporate
Allowance for credit losses
Charge-offs		(203)	(139)
Recoveries		17	12
Replenishment of net charge-offs		186	127
Net reserve builds (releases) for loans		(1,273)	1,268
Net specific reserve builds (releases)		(38)	48
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0
Other		(7)	(30)
Allowance for credit losses on loans
Collectively evaluated		3,595		4,887
Individually evaluated		489		515
Total allowance for credit losses on loans		4,084	3,451	5,402	2,886
Loans, net of unearned income
Collectively evaluated		381,338		376,677
Individually evaluated		3,106		3,527
Loans at fair value		7,510		6,840
Loans, net of unearned income		391,954		387,044
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
Charge-offs		(2,005)	(2,340)
Recoveries		443	408
Replenishment of net charge-offs		1,562	1,932
Net reserve builds (releases) for loans		(1,795)	2,826
Net specific reserve builds (releases)		(121)	176
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	4
Other		(84)	(453)
Allowance for credit losses on loans
Collectively evaluated		16,339		18,207
Individually evaluated		1,214		1,345
Total allowance for credit losses on loans		17,554	$ 16,929	19,554	9,897
Loans, net of unearned income
Collectively evaluated		269,151		283,885
Individually evaluated		4,733		4,799
Loans at fair value		15		14
Loans, net of unearned income		274,034		288,839
Consumer | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		1		2
Loans, net of unearned income
Purchased credit deteriorated		$ 135		141
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Net reserve builds (releases) for loans	$ 4,900
Allowance for credit losses on loans
Total allowance for credit losses on loans	$ 4,100			0	4,201
Cumulative Effect, Period of Adoption, Adjustment | Corporate
Allowance for credit losses on loans
Total allowance for credit losses on loans				0	(721)
Cumulative Effect, Period of Adoption, Adjustment | Consumer
Allowance for credit losses on loans
Total allowance for credit losses on loans				$ 0	$ 4,922