Derivatives (Narrative) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Notional amount of derivatives	$ 7,654,954,000	$ 7,691,719,000
Fair value liability	2,600,000	1,300,000
Credit risk-related contingent features, net liability position	72,900,000	65,600,000
Credit risk-related contingent features, posted collateral	72,500,000	66,000,000
Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Notional amount of derivatives	2,027,500,000	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	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	$ 475,000,000
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	$ 925,000,000
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	$ 100,000,000
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	443,100,000
Basis adjustment associated with hedged items loss	34,400,000
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	$ 514,300,000