BORROWINGS - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Debt Instrument [Line Items]
Short-term advances	$ 930,000,000	$ 930,000,000		$ 1,000,000,000
Short-term advances, percentage bearing fixed interest rate	100.00%	100.00%		100.00%
Other subordinated debt	$ 274,000,000	$ 274,000,000		$ 248,000,000
Subordinated notes	66,000,000	66,000,000		68,000,000
Aggregate principal amount	933,000,000	933,000,000
Proceeds from debt, net of issuance costs		933,000,000
Repayments of debt		223,000,000	$ 227,000,000
Long-term borrowings	1,059,000,000	1,059,000,000		682,000,000
FHLB
Debt Instrument [Line Items]
Credit available with FHLB	9,400,000,000	9,400,000,000
Credit with FHLB utilized	900,000,000	900,000,000
Long-term borrowings	0	0		0
FHLB
Debt Instrument [Line Items]
Short-term advances	0	0		$ 0
Minimum | FHLB
Debt Instrument [Line Items]
Effective interest rates				0.26%
Maximum | FHLB
Debt Instrument [Line Items]
Effective interest rates				0.29%
5.150% Senior Notes due August 25, 2025
Debt Instrument [Line Items]
Aggregate principal amount	$ 350,000,000	$ 350,000,000
Interest rate	5.15%	5.15%
Proceeds from debt, net of issuance costs	$ 347,400,000	$ 347,000,000
2.200% Senior Notes due February 24, 2023
Debt Instrument [Line Items]
Aggregate principal amount	$ 300,000,000	$ 300,000,000
Interest rate	2.20%	2.20%
Proceeds from debt, net of issuance costs		$ 298,000,000
Repayments of debt	$ 300,000,000
Howard
Debt Instrument [Line Items]
Other subordinated debt	25,000,000	25,000,000
Subordinated notes	$ 5,000,000	$ 5,000,000