FAIR VALUE (Fair Value Measurements, Recurring) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
AFS investment securities	$ 11,078,972	$ 14,339,758
Other investments - trading securities	42,464	1,097
RICs held-for-investment	61,400	102,000
LHFS	240,200	289,000
Other assets - derivatives	1,403,599	555,896
Financial liabilities:
Other liabilities - derivatives	1,216,524	537,008
Total MSRs	81,776	132,683
U.S. Treasury securities
Financial assets:
AFS investment securities	215,654	4,090,938
Corporate debt
Financial assets:
AFS investment securities	172,908	139,713
ABS
Financial assets:
AFS investment securities	111,141	138,400
State and municipal securities
Financial assets:
AFS investment securities	3	9
Recurring
Financial assets:
AFS investment securities	11,078,972	14,339,758
Other investments - trading securities	42,464	1,097
RICs held-for-investment	61,448	101,968
LHFS	240,190	289,009
MSRs	81,776	130,855
Other assets - derivatives	1,403,599	556,331
Total financial assets	12,908,449	15,419,018
Financial liabilities:
Other liabilities - derivatives	1,220,385	546,414
Total financial liabilities	1,220,385	546,414
Recurring \| U.S. Treasury securities
Financial assets:
AFS investment securities	215,654	4,090,938
Recurring \| Corporate debt
Financial assets:
AFS investment securities	172,908	139,713
Recurring \| ABS
Financial assets:
AFS investment securities	111,141	138,400
Recurring \| State and municipal securities
Financial assets:
AFS investment securities	3	9
Recurring \| MBS
Financial assets:
AFS investment securities	10,579,266	9,970,698
Recurring \| Level 1
Financial assets:
AFS investment securities	0	0
Other investments - trading securities	2,359	379
RICs held-for-investment	0	0
LHFS	0	0
MSRs	0	0
Other assets - derivatives	0	0
Total financial assets	2,359	379
Financial liabilities:
Other liabilities - derivatives	0	0
Total financial liabilities	0	0
Recurring \| Level 1 \| U.S. Treasury securities
Financial assets:
AFS investment securities	0	0
Recurring \| Level 1 \| Corporate debt
Financial assets:
AFS investment securities	0	0
Recurring \| Level 1 \| ABS
Financial assets:
AFS investment securities	0	0
Recurring \| Level 1 \| State and municipal securities
Financial assets:
AFS investment securities	0	0
Recurring \| Level 1 \| MBS
Financial assets:
AFS investment securities	0	0
Recurring \| Level 2
Financial assets:
AFS investment securities	11,028,406	14,276,523
Other investments - trading securities	40,105	718
RICs held-for-investment	0	17,634
LHFS	240,190	289,009
MSRs	0	0
Other assets - derivatives	1,387,232	553,222
Total financial assets	12,695,933	15,137,106
Financial liabilities:
Other liabilities - derivatives	1,214,548	543,560
Total financial liabilities	1,214,548	543,560
Recurring \| Level 2 \| U.S. Treasury securities
Financial assets:
AFS investment securities	215,654	4,090,938
Recurring \| Level 2 \| Corporate debt
Financial assets:
AFS investment securities	172,908	139,713
Recurring \| Level 2 \| ABS
Financial assets:
AFS investment securities	60,575	75,165
Recurring \| Level 2 \| State and municipal securities
Financial assets:
AFS investment securities	3	9
Recurring \| Level 2 \| MBS
Financial assets:
AFS investment securities	10,579,266	9,970,698
Recurring \| Level 3
Financial assets:
AFS investment securities	50,566	63,235
Other investments - trading securities	0	0
RICs held-for-investment	61,448	84,334
LHFS	0	0
MSRs	81,776	130,855
Other assets - derivatives	16,367	3,109
Total financial assets	210,157	281,533
Financial liabilities:
Other liabilities - derivatives	5,837	2,854
Total financial liabilities	$ 5,837	2,854
Percentage of level 3 assets to total assets held at fair value	1.60%
Percentage of level 3 assets to total assets	0.10%
Recurring \| Level 3 \| U.S. Treasury securities
Financial assets:
AFS investment securities	$ 0	0
Recurring \| Level 3 \| Corporate debt
Financial assets:
AFS investment securities	0	0
Recurring \| Level 3 \| ABS
Financial assets:
AFS investment securities	50,566	63,235
Recurring \| Level 3 \| State and municipal securities
Financial assets:
AFS investment securities	0	0
Recurring \| Level 3 \| MBS
Financial assets:
AFS investment securities	$ 0	$ 0

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Percentage of Level 3 assets to total assets held at fair value

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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