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Derivatives (Narrative) (Details) - USD ($)
3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Derivative [Line Items]      
Notional amount of derivatives $ 7,273,317,000   $ 7,392,532,000
Fair value hedges resulting net earnings (4,517,000) $ (11,967,000)  
Fair value liability 2,100,000   2,100,000
Credit risk-related contingent features, net liability position 28,200,000   39,100,000
Credit risk-related contingent features, posted collateral 28,300,000   38,000,000
Fair Value Hedging [Member]      
Derivative [Line Items]      
Fair value hedges resulting net earnings 163,500,000    
Derivatives Designated as Hedging Instruments [Member]      
Derivative [Line Items]      
Notional amount of derivatives 1,977,500,000   1,827,500,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 3, Expires 2025 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 50,000,000    
Derivative maturity expiration year 2025    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 4, Expires 2026 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 425,000,000    
Derivative maturity expiration year 2026    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 5, Expires 2027 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 825,000,000    
Derivative maturity expiration year 2027    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 6, Expires 2028 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 50,000,000    
Derivative maturity expiration year 2028    
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 7, Expires 2029 [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 150,000,000    
Derivative maturity expiration year 2029    
Interest Rate Swaps - Securities [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member]      
Derivative [Line Items]      
Notional amount of derivatives $ 477,500,000   $ 477,500,000
Fair value hedges resulting net earnings 3,910,000 $ 3,108,000  
Derivative hedged item 445,600,000    
Basis adjustment associated with hedged items loss 31,900,000    
Interest Rate Swaps - Securities [Member] | Derivatives Designated as Hedging Instruments [Member] | Fair Value Hedging [Member] | Commercial Mortgage-Backed Securities [Member]      
Derivative [Line Items]      
Amortized cost basis of closed portfolio of pre-payable securities $ 514,000,000