Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Derivative [Line Items]
Net unrealized gains (losses) arising during the period	$ (39,096,000)	$ (111,549,000)	$ (102,218,000)	$ (284,216,000)
(Loss) income recognized	(6,200,000)	690,000	(17,700,000)	3,900,000
Cash flow hedge loss to be reclassified			155,000,000
Cash flow hedge termination loss			22,000,000
Right to reclaim cash collateral	77,500,000		77,500,000		$ 66,800,000
Obligation to return cash collateral	5,700,000		5,700,000		$ 7,700,000
Cash Flow Hedges
Derivative [Line Items]
Net unrealized gains (losses) arising during the period	0	$ 0	$ 0	$ 0
Fair Value Hedges | Interest Rate Contract | Long-term debt
Derivative [Line Items]
Hedged liability, discontinued fair value hedge	347,600,000
Fair Value Hedges | Interest Rate Contract | Interest-bearing deposits
Derivative [Line Items]
Hedged liability, discontinued fair value hedge	$ 150,000,000