ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Allowance for credit losses
Charge-offs		$ (2,528)	$ (2,354)	$ (5,007)	$ (4,699)
Recoveries		322	391	693	788
Replenishment of net charge-offs		2,206	1,963	4,314	3,911
Net reserve builds (releases)		4,856	53	8,968	120
Net specific reserve builds (releases)		634	73	858	2
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other		89	11	(394)	29
Allowance for credit losses on loans
Collectively evaluated		24,400		24,400			$ 11,293
Individually evaluated		2,015		2,015			1,489
Total allowance for credit losses on loans		26,420	12,466	26,420	12,466	$ 20,841	12,783	$ 12,329	$ 12,315
Loans, net of unearned income
Collectively evaluated		670,850		670,850			688,338
Individually evaluated		8,522		8,522			6,932
Loans at fair value		5,799		5,799			4,085
Loans, net of unearned income		685,292		685,292			699,483
Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		5		5			1
Loans, net of unearned income
Purchased credit deteriorated		121		121			128
Corporate
Allowance for credit losses
Charge-offs		(347)	(104)	(485)	(204)
Recoveries		23	15	34	36
Replenishment of net charge-offs		324	89	451	168
Net reserve builds (releases)		2,883	50	4,151	54
Net specific reserve builds (releases)		486	3	534	(76)
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	0	0
Other		4	3	(26)	(2)
Allowance for credit losses on loans
Collectively evaluated		6,056		6,056			2,587
Individually evaluated		768		768			299
Total allowance for credit losses on loans		6,824	2,787	6,824	2,787	3,451	2,886	2,731	2,811
Loans, net of unearned income
Collectively evaluated		394,380		394,380			383,828
Individually evaluated		4,016		4,016			2,040
Loans at fair value		5,783		5,783			4,067
Loans, net of unearned income		404,179		404,179			389,935
Corporate | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		0		0			0
Loans, net of unearned income
Purchased credit deteriorated		0		0			0
Consumer
Allowance for credit losses
Charge-offs		(2,181)	(2,250)	(4,522)	(4,495)
Recoveries		299	376	659	752
Replenishment of net charge-offs		1,882	1,874	3,863	3,743
Net reserve builds (releases)		1,973	3	4,817	66
Net specific reserve builds (releases)		148	70	324	78
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other		85	8	(368)	31
Allowance for credit losses on loans
Collectively evaluated		18,344		18,344			8,706
Individually evaluated		1,247		1,247			1,190
Total allowance for credit losses on loans		19,596	$ 9,679	19,596	$ 9,679	17,390	9,897	$ 9,598	9,504
Loans, net of unearned income
Collectively evaluated		276,470		276,470			304,510
Individually evaluated		4,506		4,506			4,892
Loans at fair value		16		16			18
Loans, net of unearned income		281,113		281,113			309,548
Consumer | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		5		5			1
Loans, net of unearned income
Purchased credit deteriorated		$ 121		$ 121			128
Cumulative Effect, Period of Adoption, Adjustment
Allowance for credit losses
Net reserve builds (releases)	$ 4,900
Allowance for credit losses on loans
Total allowance for credit losses on loans	$ 4,100					$ 0	4,201		0
Cumulative Effect, Period of Adoption, Adjustment | Corporate
Allowance for credit losses on loans
Total allowance for credit losses on loans							(721)		0
Cumulative Effect, Period of Adoption, Adjustment | Consumer
Allowance for credit losses on loans
Total allowance for credit losses on loans							$ 4,922		$ 0