FINANCIAL DERIVATIVES - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2026	Dec. 31, 2025
Notional Disclosures [Abstract]
Notional Amount	$ 30,094,623	$ 25,577,094
Asset
Fair value, asset	19,912	44,875
Netting adjustments	(979)	(1,631)
(Liability)
Fair value, liability	(219,897)	(21,618)
Netting adjustments	979	1,631
Receive fixed non-callable | No hedge designation
Notional Disclosures [Abstract]
Notional Amount	1,179,477	1,963,363
Asset
Fair value, asset	63	66
(Liability)
Fair value, liability	$ (1)	$ (9)
Weighted- Average Pay Rate	3.95%	3.89%
Weighted- Average Receive Rate	3.75%	3.93%
Weighted- Average Remaining Term (in years)	3 months	3 months 10 days
Receive fixed non-callable | Fair value hedges: | Designated as hedge
Notional Disclosures [Abstract]
Notional Amount	$ 7,217,985	$ 10,681,418
Asset
Fair value, asset	1,331	16,685
(Liability)
Fair value, liability	$ (1,847)	$ (168)
Weighted- Average Pay Rate	4.10%	2.79%
Weighted- Average Receive Rate	3.85%	3.93%
Weighted- Average Remaining Term (in years)	11 months 23 days	8 years 7 months 28 days
Pay fixed non-callable | No hedge designation
Notional Disclosures [Abstract]
Notional Amount	$ 154,391	$ 159,684
Asset
Fair value, asset	731	613
(Liability)
Fair value, liability	$ (61)	$ (1)
Weighted- Average Pay Rate	2.85%	2.88%
Weighted- Average Receive Rate	4.16%	4.13%
Weighted- Average Remaining Term (in years)	3 years 14 days	3 years 7 months 9 days
Pay fixed non-callable | Fair value hedges: | Designated as hedge
Notional Disclosures [Abstract]
Notional Amount	$ 12,382,796	$ 6,388,935
Asset
Fair value, asset	9,465	330
(Liability)
Fair value, liability	$ (870)	$ (2,954)
Weighted- Average Pay Rate	3.00%	4.08%
Weighted- Average Receive Rate	3.94%	3.56%
Weighted- Average Remaining Term (in years)	8 years 4 months 2 days	1 year 1 month 13 days
Pay fixed non-callable | Cash flow hedges: | Designated as hedge
Notional Disclosures [Abstract]
Notional Amount	$ 392,000	$ 452,000
Asset
Fair value, asset	9,298	9,335
(Liability)
Fair value, liability	$ (25)	$ (1)
Weighted- Average Pay Rate	1.88%	1.92%
Weighted- Average Receive Rate	4.34%	4.22%
Weighted- Average Remaining Term (in years)	2 years 7 months 20 days	3 years
Receive fixed callable | Fair value hedges: | Designated as hedge
Notional Disclosures [Abstract]
Notional Amount	$ 8,414,163	$ 5,446,883
Asset
Fair value, asset	0	19,322
(Liability)
Fair value, liability	$ (217,975)	$ (19,911)
Weighted- Average Pay Rate	4.00%	3.96%
Weighted- Average Receive Rate	3.98%	3.73%
Weighted- Average Remaining Term (in years)	3 years 4 months 24 days	3 years 1 month 20 days
Basis swaps | No hedge designation
Notional Disclosures [Abstract]
Notional Amount	$ 347,811	$ 382,811
Asset
Fair value, asset	3	1
(Liability)
Fair value, liability	$ (53)	$ (190)
Weighted- Average Pay Rate	4.13%	4.13%
Weighted- Average Receive Rate	4.07%	3.89%
Weighted- Average Remaining Term (in years)	4 years 9 months	5 years 10 days
Treasury futures | No hedge designation
Notional Disclosures [Abstract]
Notional Amount	$ 6,000	$ 102,000
Asset
Fair value, asset	0	154
Netting adjustments	(979)	(1,631)
(Liability)
Fair value, liability	(44)	(15)
Netting adjustments	$ 979	$ 1,631
Weighted- Average Forward Price (in dollars per share)	$ 104.94	$ 112.57