INVESTMENT SECURITIES - Narrative (Details)	3 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($)	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Gain (Loss) on Securities [Line Items]
Trading securities		$ 0
Number of available for sale investment securities | security		966
Number of available-for-sale securities unrealized loss position | security		957
Weighted average duration of MBS portfolio		5 years 9 months 18 days
Securities transferred to held-to-maturity from available-for-sale at fair value		$ 0	$ 931,421,000	$ 0
Securities pledged as collateral		3,300,000,000	2,800,000,000
Sale of investment securities available-for-sale		0	0	14,051,000
Gain on sale of investment securities available for sale				300,000
Losses from sale of available-for-sale securities				$ 0
Unamortized premiums		56,900,000	66,600,000
Unaccreted discounts		20,900,000	25,200,000
Owned investment securities		3,800,000,000
Total unrealized losses on securities		658,000,000
Allowance for credit losses		0	0
Held-to-maturity debt securities with an amortized cost basis		1,100,000,000	1,100,000,000
Accrued interest		3,700,000	2,400,000
Debt securities nonaccrual		0	0
Past due held-to-maturity debt securities		1,058,565,000	1,111,629,000
Past Due
Gain (Loss) on Securities [Line Items]
Past due held-to-maturity debt securities		0	0
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Gain (Loss) on Securities [Line Items]
Securities transferred to held-to-maturity from available-for-sale, book value	$ 1,100,000,000	1,100,000,000
Securities transferred to held-to-maturity from available-for-sale at fair value	931,400,000
Available for sale securities transfers to held to maturity unrealized (losses) gains	$ 157,600,000
Allowance for credit losses		0	0
Past due held-to-maturity debt securities		$ 872,653,000	$ 909,498,000