ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward by Segment (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Allowance for credit losses
Charge-offs		$ (2,367)	$ (2,281)	$ (7,374)	$ (6,980)
Recoveries		448	368	1,141	1,156
Replenishment of net charge-offs		1,919	1,913	6,233	5,824
Net reserve builds (releases) for loans		42	132	9,010	252
Net specific reserve builds (releases)		(152)	17	706	19
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other		116	(85)	(278)	(56)
Allowance for credit losses on loans
Collectively evaluated		24,562		24,562			$ 11,293
Individually evaluated		1,861		1,861			1,489
Total allowance for credit losses on loans		26,426	12,530	26,426	12,530	$ 26,420	12,783	$ 12,466	$ 12,315
Loans, net of unearned income
Collectively evaluated		653,139		653,139			688,338
Individually evaluated		8,109		8,109			6,932
Loans at fair value		5,524		5,524			4,085
Loans, net of unearned income		666,911		666,911			699,483
Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		3		3			1
Loans, net of unearned income
Purchased credit deteriorated		139		139			128
Corporate
Allowance for credit losses
Charge-offs		(351)	(129)	(836)	(333)
Recoveries		26	19	60	55
Replenishment of net charge-offs		325	110	776	278
Net reserve builds (releases) for loans		267	37	4,418	91
Net specific reserve builds (releases)		(161)	(1)	373	(77)
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	0	0
Other		8	(20)	(18)	(22)
Allowance for credit losses on loans
Collectively evaluated		6,340		6,340			2,587
Individually evaluated		598		598			299
Total allowance for credit losses on loans		6,938	2,803	6,938	2,803	6,824	2,886	2,787	2,811
Loans, net of unearned income
Collectively evaluated		377,792		377,792			383,828
Individually evaluated		3,584		3,584			2,040
Loans at fair value		5,510		5,510			4,067
Loans, net of unearned income		386,886		386,886			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		(2,016)	(2,152)	(6,538)	(6,647)
Recoveries		422	349	1,081	1,101
Replenishment of net charge-offs		1,594	1,803	5,457	5,546
Net reserve builds (releases) for loans		(225)	95	4,592	161
Net specific reserve builds (releases)		9	18	333	96
Initial allowance for credit losses on newly purchased credit deteriorated assets during the period		0	0	4	0
Other		108	(65)	(260)	(34)
Allowance for credit losses on loans
Collectively evaluated		18,222		18,222			8,706
Individually evaluated		1,263		1,263			1,190
Total allowance for credit losses on loans		19,488	$ 9,727	19,488	$ 9,727	19,596	9,897	$ 9,679	9,504
Loans, net of unearned income
Collectively evaluated		275,347		275,347			304,510
Individually evaluated		4,525		4,525			4,892
Loans at fair value		14		14			18
Loans, net of unearned income		280,025		280,025			309,548
Consumer | Purchased Credit Deteriorated
Allowance for credit losses on loans
Purchased credit deteriorated		3		3			1
Loans, net of unearned income
Purchased credit deteriorated		$ 139		$ 139			128
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		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