INVESTMENT SECURITIES (Securities Pledged as Collateral) (Details) - USD ($)	6 Months Ended	12 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	$ 5,000,000,000.0	$ 7,500,000,000
Accrued interest on investment securities	40,400,000	46,000,000.0
AFS investment securities transferred to HTM investment securities	0	0
Collateral with Federal Reserve Bank
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	359,200,000	2,700,000,000
Public fund deposits
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	3,800,000,000	3,500,000,000
Repurchase agreements, hedging activities and recourse on loan sales
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	129,700,000	148,500,000
Deposits with Clearing Organizations
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	350,000,000.0	699,100,000
Overnight customer deposits
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral, fair value	$ 425,900,000	$ 461,900,000

Debt Securities, Available-For-Sale, Transferred To Held-To-Maturity Securities

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Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

+ References

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+ References

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Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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