INVESTMENT SECURITIES - Narrative (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2022	Sep. 30, 2021	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Debt securities, reclassified		$ 3,590,000,000
Proceeds from sale of available-for-sale securities	$ 3,160,000,000
Pre-tax loss	625,600,000
Estimated tax rate					24.70%	10.90%	12.70%
Debt securities, available-for-sale, transfer to held-to-maturity			$ 1,990,000,000	$ 500,800,000
Available-for-sale, transfer to held-to-maturity, gain (loss)					$ 0
Held to maturity mortgage backed securities						$ 3,639,850,000
Available for sale mortgage backed securities	3,642,809,000				3,642,809,000	2,852,774,000
Available-for-sale, interest receivable	23,800,000				23,800,000
Available-for-sale securities	3,266,221,000				3,266,221,000	2,529,426,000
Securities valued at less than historical cost, amount	$ 2,660,240,000				$ 2,660,240,000	2,467,223,000
Securities valued at less than historical cost (as percent)	81.40%				81.40%
Provision for credit losses, AFS					$ 0	0
Provision for credit loss expense (reversal)					(3,214,000)	0	$ 1,826,000
Securities pledged as collateral	$ 2,040,000,000.00				2,040,000,000.00	2,360,000,000
Realized gains					0	0	0
Realized losses					$ 801,500,000	$ 28,400,000	$ 20,600,000
Income tax benefit related to security gains (losses) (as percent)					21.946%	26.135%	26.135%
Variable rate commercial MBS
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities						$ 136,000,000.0
Available for sale mortgage backed securities	597,400,000				$ 597,400,000	517,200,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities						934,100,000
Available for sale mortgage backed securities	$ 1,600,000,000				$ 1,600,000,000	875,500,000
Bonds
Debt Securities, Available-for-sale [Line Items]
Investments sold, amount						$ 251,500,000	$ 247,900,000