FINANCIAL DERIVATIVES - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Notional Disclosures [Abstract]
Notional Amount	$ 26,094,494	$ 25,779,468
Asset
Fair value, asset	31,433	37,478
Netting adjustments	(3,355)	(1,236)
(Liability)
Fair value, liability	(128,530)	(117,131)
Netting adjustments	3,355	1,236
Designated as hedge | Fair value hedges: | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	9,705,185	9,174,253
Asset
Fair value, asset	230	7,767
(Liability)
Fair value, liability	$ (25,315)	$ (1,081)
Weighted- Average Pay Rate	5.54%	2.50%
Weighted- Average Receive Rate	3.03%	5.47%
Weighted- Average Remaining Term (in years)	1 year 8 months 12 days	9 years 6 months 25 days
Designated as hedge | Fair value hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 9,226,082	$ 9,776,685
Asset
Fair value, asset	7,675	2,350
(Liability)
Fair value, liability	$ (68)	$ (20,390)
Weighted- Average Pay Rate	2.52%	5.57%
Weighted- Average Receive Rate	5.43%	2.94%
Weighted- Average Remaining Term (in years)	9 years 4 months 13 days	1 year 9 months 10 days
Designated as hedge | Fair value hedges: | Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 3,963,827	$ 3,879,827
Asset
Fair value, asset	2,892	7,374
(Liability)
Fair value, liability	$ (105,971)	$ (95,984)
Weighted- Average Pay Rate	5.36%	5.40%
Weighted- Average Receive Rate	3.46%	3.40%
Weighted- Average Remaining Term (in years)	2 years 6 months 21 days	2 years 5 months 23 days
Designated as hedge | Cash flow hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 552,000	$ 558,000
Asset
Fair value, asset	22,270	20,234
(Liability)
Fair value, liability	$ 0	$ (43)
Weighted- Average Pay Rate	1.93%	1.94%
Weighted- Average Receive Rate	5.80%	5.82%
Weighted- Average Remaining Term (in years)	4 years 1 month 2 days	4 years 3 months 18 days
No hedge designation | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 1,638,958	$ 1,358,396
Asset
Fair value, asset	34	263
(Liability)
Fair value, liability	$ (9)	$ (3)
Weighted- Average Pay Rate	5.38%	5.44%
Weighted- Average Receive Rate	5.11%	4.87%
Weighted- Average Remaining Term (in years)	5 months 19 days	7 months 20 days
No hedge designation | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 157,933	$ 160,623
Asset
Fair value, asset	992	676
(Liability)
Fair value, liability	$ 0	$ (29)
Weighted- Average Pay Rate	2.92%	2.92%
Weighted- Average Receive Rate	5.60%	5.64%
Weighted- Average Remaining Term (in years)	4 years 1 month 24 days	4 years 4 months 2 days
No hedge designation | Basis swaps
Notional Disclosures [Abstract]
Notional Amount	$ 850,384	$ 850,384
Asset
Fair value, asset	15	39
(Liability)
Fair value, liability	$ (522)	$ (746)
Weighted- Average Pay Rate	5.49%	5.52%
Weighted- Average Receive Rate	5.47%	5.48%
Weighted- Average Remaining Term (in years)	3 years 6 months 29 days	3 years 9 months 29 days
No hedge designation | Treasury futures
Notional Disclosures [Abstract]
Notional Amount	$ 125	$ 21,300
Asset
Fair value, asset	680	11
Netting adjustments	(3,355)	(1,236)
(Liability)
Fair value, liability	0	(91)
Netting adjustments	$ 3,355	$ 1,236
Weighted- Average Forward Price (in dollars per share)	$ 110.25	$ 112.51