LONG-TERM BORROWINGS - Schedule of Subordinated Debt (Detail)	3 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Dec. 31, 2023 USD ($)
Debt Instrument [Line Items]
Aggregate Principal Amount Issued		$ 620,000,000
Net Proceeds		613,000,000
Carrying Value		616,000,000
Senior Notes
Debt Instrument [Line Items]
Aggregate Principal Amount Issued		350,000,000
Net Proceeds		347,000,000
Carrying Value		349,000,000
Other Subordinated Debt
Debt Instrument [Line Items]
Aggregate Principal Amount Issued		270,000,000
Net Proceeds		266,000,000
Carrying Value		$ 267,000,000
SOFR
Debt Instrument [Line Items]
Tenor spread adjustment		0.0026
5.150% Senior Notes due August 25, 2025 | Senior Notes
Debt Instrument [Line Items]
Interest Rate	5.15%	5.15%
Aggregate Principal Amount Issued	$ 350,000,000	$ 350,000,000
Net Proceeds	$ 347,400,000	347,000,000
Carrying Value		$ 349,000,000
4.950% Fixed-To-Floating Rate Subordinated Notes due 2029 | Other Subordinated Debt
Debt Instrument [Line Items]
Interest Rate		4.95%
Aggregate Principal Amount Issued		$ 120,000,000
Net Proceeds		118,000,000
Carrying Value		$ 119,000,000
4.950% Fixed-To-Floating Rate Subordinated Notes due 2029 | SOFR | Other Subordinated Debt
Debt Instrument [Line Items]
Rate Reset Factor		2.40%
Tenor spread adjustment		0.0026
4.875% Subordinated Notes due 2025 | Other Subordinated Debt
Debt Instrument [Line Items]
Interest Rate		4.875%
Aggregate Principal Amount Issued		$ 100,000,000
Net Proceeds		98,000,000
Carrying Value		$ 100,000,000
Fixed-To-Floating Rate Subordinated Notes due December 6, 2028 | Other Subordinated Debt
Debt Instrument [Line Items]
Interest Rate		8.645%
Aggregate Principal Amount Issued		$ 25,000,000
Net Proceeds		26,000,000
Carrying Value		$ 24,000,000
Fixed-To-Floating Rate Subordinated Notes due December 6, 2028 | SOFR | Other Subordinated Debt
Debt Instrument [Line Items]
Rate Reset Factor		3.02%
Tenor spread adjustment		0.0026
5.00% Fixed-To-Floating Rate Subordinated Note due May 29, 2030 | Other Subordinated Debt
Debt Instrument [Line Items]
Interest Rate		5.00%
Aggregate Principal Amount Issued		$ 25,000,000
Net Proceeds		24,000,000
Carrying Value		$ 24,000,000
5.00% Fixed-To-Floating Rate Subordinated Note due May 29, 2030 | SOFR | Other Subordinated Debt
Debt Instrument [Line Items]
Rate Reset Factor		4.64%