LOANS AND ALLOWANCE FOR CREDIT LOSSES (Rollforward of Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Jun. 30, 2020
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)	$ 7,112,738		$ 3,783,833	$ 3,646,189	[1]	$ 3,897,130
Credit loss expense on loans	380,596		597,891	2,523,073		1,684,828
Charge-offs	(606,141)		(1,424,680)	(2,847,535)		(4,138,436)
Recoveries	512,405		778,816	1,541,989		2,292,338
Charge-offs, net of recoveries	(93,736)		(645,864)	(1,305,546)		(1,846,098)
ALLL, end of period	7,399,598	[1]	3,735,860	7,399,598	[1]	3,735,860
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)	122,743		89,406	91,826		95,500
Credit loss expense on unfunded lending commitments	25,229		5,744	45,735		(350)
Reserve for unfunded lending commitments, end of period	147,972		95,150	147,972		95,150
Total ACL, end of period	7,547,570		3,831,010	7,547,570		3,831,010
Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)				2,535,882
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)				10,411
Commercial
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)	759,599		447,078	399,829		441,086
Credit loss expense on loans	14,797		14,251	254,262		59,895
Charge-offs	(28,962)		(57,276)	(125,871)		(117,591)
Recoveries	7,843		18,393	26,138		39,056
Charge-offs, net of recoveries	(21,119)		(38,883)	(99,733)		(78,535)
ALLL, end of period	753,277		422,446	753,277		422,446
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)	95,022		83,346	85,934		89,472
Credit loss expense on unfunded lending commitments	24,752		5,907	23,759		(219)
Reserve for unfunded lending commitments, end of period	119,774		89,253	119,774		89,253
Total ACL, end of period	873,051		511,699	873,051		511,699
Financing receivable, allowance for credit loss, reclassification							$ (322,000)
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)				198,919
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)				10,081
Consumer
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)	6,353,139		3,290,007	3,199,612		3,409,021
Credit loss expense on loans	365,799		583,640	2,268,811		1,624,933
Charge-offs	(577,179)		(1,367,404)	(2,721,664)		(4,020,570)
Recoveries	504,562		760,423	1,515,851		2,253,282
Charge-offs, net of recoveries	(72,617)		(606,981)	(1,205,813)		(1,767,288)
ALLL, end of period	6,646,321		3,266,666	6,646,321		3,266,666
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)	27,721		6,060	5,892		6,028
Credit loss expense on unfunded lending commitments	477		(163)	21,976		(131)
Reserve for unfunded lending commitments, end of period	28,198		5,897	28,198		5,897
Total ACL, end of period	6,674,519		3,272,563	6,674,519		3,272,563
Transfer of LHFI to LHFS			0			20,400
Financing receivable, allowance for credit loss, reclassification							$ 322,000
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)				2,383,711
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)				330
Unallocated
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)	0		46,748	46,748		47,023
Credit loss expense on loans			0			0
Charge-offs			0			(275)
Recoveries			0			0
Charge-offs, net of recoveries	0		0	0		(275)
ALLL, end of period	0		46,748	0		46,748
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)			0			0
Credit loss expense on unfunded lending commitments			0			0
Reserve for unfunded lending commitments, end of period	0		0	0		0
Total ACL, end of period	$ 0		$ 46,748	0		$ 46,748
Unallocated | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period (1)				(46,748)
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period (1)

[1] The Company has interests in certain Trusts that are considered VIEs for accounting purposes. At September 30, 2020 and December 31, 2019, LHFI included $22.7 billion and $26.5 billion, Operating leases assets, net included $16.2 billion and $16.5 billion, restricted cash included $1.8 billion and $1.6 billion, other assets included $870.2 million and $625.4 million, Borrowings and other debt obligations included $31.3 billion and $34.2 billion, and Other liabilities included $118.0 million and $188.1 million of assets or liabilities that were included within VIEs, respectively. See Note 7 to these Condensed Consolidated Financial Statements for additional information.