LOANS AND ALLOWANCE FOR CREDIT LOSSES (Rollforward of Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period	$ 6,623,736		$ 3,843,095	$ 3,646,189	[1]	$ 3,897,130
Credit loss expense on loans	1,024,570		463,517	2,142,477		1,066,543
Charge-offs	(943,219)		(1,244,867)	(2,241,394)		(2,693,361)
Recoveries	407,652		722,088	1,029,584		1,513,521
Charge-offs, net of recoveries	(535,567)		(522,779)	(1,211,810)		(1,179,840)
ALLL, end of period	7,112,739	[1]	3,783,833	7,112,739	[1]	3,783,833
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period	169,940		92,685	91,826		95,500
Credit loss expense on unfunded lending commitments	(47,197)		(3,280)	20,506		(6,095)
Reserve for unfunded lending commitments, end of period	122,743		89,405	122,743		89,405
Total ACL, end of period	7,235,482		3,873,238	7,235,482		3,873,238
Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period				2,535,883
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period				10,411
Commercial
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period	911,463		447,991	399,829		441,086
Credit loss expense on loans	205,488		23,671	608,316		45,644
Charge-offs	(43,446)		(36,715)	(96,908)		(60,316)
Recoveries	7,617		12,131	18,295		20,664
Charge-offs, net of recoveries	(35,829)		(24,584)	(78,613)		(39,652)
ALLL, end of period	1,081,122		447,078	1,081,122		447,078
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period	140,631		86,563	85,934		89,472
Credit loss expense on unfunded lending commitments	(45,450)		(3,218)	(834)		(6,127)
Reserve for unfunded lending commitments, end of period	95,181		83,345	95,181		83,345
Total ACL, end of period	1,176,303		530,423	1,176,303		530,423
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period				151,590
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period				10,081
Consumer
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period	5,712,273		3,348,356	3,199,612		3,409,021
Credit loss expense on loans	819,082		439,846	1,534,161		1,020,899
Charge-offs	(899,773)		(1,208,152)	(2,144,486)		(2,632,770)
Recoveries	400,035		709,957	1,011,289		1,492,857
Charge-offs, net of recoveries	(499,738)		(498,195)	(1,133,197)		(1,139,913)
ALLL, end of period	6,031,617		3,290,007	6,031,617		3,290,007
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period	29,309		6,122	5,892		6,028
Credit loss expense on unfunded lending commitments	(1,747)		(62)	21,340		32
Reserve for unfunded lending commitments, end of period	27,562		6,060	27,562		6,060
Total ACL, end of period	6,059,179		3,296,067	6,059,179		3,296,067
Transfer of LHFI to LHFS			20,400			20,400
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period				2,431,041
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period				330
Unallocated
Allowance for Loan Losses [Roll Forward]
ALLL, beginning of period	0		46,748	46,748		47,023
Credit loss expense on loans	0		0	0		0
Charge-offs	0		0	0		(275)
Recoveries	0		0	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	0		0	0		0
Credit loss expense on unfunded lending commitments	0		0	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				(46,748)
Reserve for Unfunded Lending Commitments Roll Forward [Roll Forward]
Reserve for unfunded lending commitments, beginning of period				$ 0

[1] The Company has interests in certain Trusts that are considered VIEs for accounting purposes. At June 30, 2020 and December 31, 2019, LHFI included $22.5 billion and $26.5 billion, Operating leases assets, net included $16.2 billion and $16.5 billion, restricted cash included $1.6 billion and $1.6 billion, other assets included $703.2 million and $625.4 million, Borrowings and other debt obligations included $32.3 billion and $34.2 billion, and Other liabilities included $101.1 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.