FAIR VALUE (Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial assets:
AFS investment securities	$ 12,047,923	$ 14,339,758
Investments in debt securities HTM	5,414,720	3,957,227
Other investments - trading securities	19,766	1,097
LHFS	241,300	289,000
Derivatives	1,644,784	555,896
Financial liabilities:
Derivatives	1,424,258	537,008
Carrying Value
Financial assets:
Cash and cash equivalents	11,085,206	7,644,372
AFS investment securities	12,047,923	14,339,758
Investments in debt securities HTM	5,229,562	3,938,797
Other investments - trading securities	769,766	1,097
LHFI, net	84,181,092	89,059,251
LHFS	5,439,364	1,420,223
Restricted cash	5,189,766	3,881,880
MSRs	90,231	132,683
Derivatives	1,645,386	556,331
Financial liabilities:
Deposits	5,528,540	9,375,281
Borrowings and other debt obligations	49,857,326	50,654,406
Derivatives	1,434,883	546,414
Fair Value
Financial assets:
Cash and cash equivalents	11,085,206	7,644,372
AFS investment securities	12,047,923	14,339,758
Investments in debt securities HTM	5,414,720	3,957,227
Other investments - trading securities	769,766	1,097
LHFI, net	88,368,326	90,490,760
LHFS	5,439,364	1,420,295
Restricted cash	5,189,766	3,881,880
MSRs	95,992	139,052
Derivatives	1,645,386	556,331
Financial liabilities:
Deposits	5,575,162	9,384,994
Borrowings and other debt obligations	50,291,535	51,232,798
Derivatives	1,434,883	546,414
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	11,085,206	7,644,372
AFS investment securities	0	0
Investments in debt securities HTM	0	0
Other investments - trading securities	0	379
LHFI, net	0	0
LHFS	0	0
Restricted cash	5,189,766	3,881,880
MSRs	0	0
Derivatives	0	0
Financial liabilities:
Deposits	0	0
Borrowings and other debt obligations	0	0
Derivatives	0	0
Fair Value | Level 2
Financial assets:
Cash and cash equivalents	0	0
AFS investment securities	11,997,259	14,276,523
Investments in debt securities HTM	5,414,720	3,957,227
Other investments - trading securities	769,766	718
LHFI, net	52,195	1,142,998
LHFS	241,353	289,009
Restricted cash	0	0
MSRs	0	0
Derivatives	1,628,619	553,222
Financial liabilities:
Deposits	5,575,162	9,384,994
Borrowings and other debt obligations	33,991,246	36,114,404
Derivatives	1,428,086	543,560
Fair Value | Level 3
Financial assets:
Cash and cash equivalents	0	0
AFS investment securities	50,664	63,235
Investments in debt securities HTM	0	0
Other investments - trading securities	0	0
LHFI, net	88,316,131	89,347,762
LHFS	5,198,011	1,131,286
Restricted cash	0	0
MSRs	95,992	139,052
Derivatives	16,767	3,109
Financial liabilities:
Deposits	0	0
Borrowings and other debt obligations	16,300,289	15,118,394
Derivatives	$ 6,797	$ 2,854