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Derivatives (Narrative) (Details) - USD ($)
9 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Dec. 31, 2023
Derivative [Line Items]      
Notional amount of derivatives $ 7,448,608,000   $ 7,691,719,000
Fair value liability 2,300,000   1,300,000
Credit risk-related contingent features, net liability position 30,200,000   65,600,000
Credit risk-related contingent features, posted collateral 28,700,000   66,000,000
Derivatives Designated as Hedging Instruments [Member]      
Derivative [Line Items]      
Notional amount of derivatives 1,827,500,000   2,027,500,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member]      
Derivative [Line Items]      
Amortization of accumulated other comprehensive loss on terminated cash flow hedges 13,700,000 $ 2,900,000  
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] | Fair Value Hedging [Member]      
Derivative [Line Items]      
Amortization of accumulated other comprehensive loss on terminated cash flow hedges   $ 16,600,000  
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
Derivative hedged item 455,300,000    
Basis adjustment associated with hedged items loss 22,200,000    
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 $ 514,200,000