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Securities - Additional Information (Detail) - USD ($)
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Dec. 31, 2022
Schedule of Trading Securities and Other Trading Assets [Line Items]        
Proceeds from sales of securities available for sale $ 51,771,000 $ 611,423,000    
Fair Value 13,660,886,000   $ 13,709,141,000  
Gross realized gains from securities 403,000 390,000    
Accrued interest on securities available for sale 74,500,000   82,900,000  
ACL related to AFS Securities 0   0  
Sales of securities held to maturity 0 0    
Amortized cost of available for sale securities transferred to held to maturity       $ 4,100,000,000
Fair value of available for sale securities transferred to held to maturity       $ 3,800,000,000
Gain (loss) on transfer of securities 0      
Unamortized unrealized loss 132,100,000   139,200,000  
Accrued interest on securities held to maturity 25,200,000   28,000,000  
Unrealized gain (loss) on trading securities (6,000) $ (15,000)    
Securities sold not yet purchased 8,300,000   4,100,000  
Securities held to maturity with an acquired fair value 5,172,564,000   5,250,465,000  
Other securities 685,590,000   676,300,000  
Collateral Pledged [Member] | U.S. Government and Other Public Deposit [Member]        
Schedule of Trading Securities and Other Trading Assets [Line Items]        
Pledged securities for deposits $ 12,700,000,000   $ 13,400,000,000