INVESTMENTS - Narrative (Details)	3 Months Ended
	Mar. 31, 2022 USD ($) security	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Trading securities	$ 0
Number of available for sale investment securities | security	1,089
Number of available-for-sale securities unrealized loss position | security	934
Weighted average duration of MBS portfolio	5 years 6 months
Sale of investment securities available for sale, including interest	$ 0	$ 9,300,000
Debt securities, available-for-sale, realized gain	0	300,000
Losses from sale of available-for-sale securities	0	0
Unamortized premiums	66,900,000		$ 69,400,000
Unaccreted discounts	18,000,000		12,700,000
Owned investment securities	5,200,000,000
Total unrealized losses on securities	411,300,000
Allowance for credit losses	0		0
Held-to-maturity debt securities with an amortized cost basis	84,900,000		90,600,000
Accrued interest	700,000		900,000
Debt securities nonaccrual	0		0
Equity investments	13,700,000		10,500,000
Unrealized gain (loss) on equity investments, net	(3,000)	$ 0
Collateral Pledged
Debt Securities, Available-for-sale [Line Items]
Securities pledged as collateral	$ 2,700,000,000		$ 2,200,000,000