INVESTMENT SECURITIES - Investment securities pledged as collateral (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Investment securities pledged as collateral
Investment securities pledged to collateralize certain deposits and borrowings	$ 2,180.0	$ 2,320.0
Debt Securities, Pledged Status [Extensible Enumeration]	us-gaap:AssetPledgedAsCollateralWithoutRightMember	us-gaap:AssetPledgedAsCollateralWithoutRightMember
Debt Securities, Pledging Purpose [Extensible Enumeration]	Deposits	Deposits
U.S. Treasury and agency securities \| Securities Sold under Agreements to Repurchase
Investment securities pledged as collateral
Investment securities pledged to collateralize certain deposits and borrowings	$ 466.9	$ 485.4

Indicates pledged status of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI https://asc.fasb.org/extlink&oid=123419778&loc=d3e5710-111685

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI https://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_DebtSecuritiesPledgedStatusExtensibleEnumeration
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant