Securities (Narrative) (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) security	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) security	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) security
Unrealized Loss
Number of available-for-sale debt securities in an unrealized loss position | security	359		359		104
Available-for-sale debt securities, in gross unrealized loss position			$ 0		$ 0
Debt Securities, AFS, allowance for credit loss	$ 0		0		$ 0
(Reversal of) provision for credit losses	(10,000,000)	$ 10,000,000	(25,000,000)	$ 186,313,000
AFS debt securities
Unrealized Loss
(Reversal of) provision for credit losses	$ 0	$ 0	$ 0	$ 0
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities
Unrealized Loss
Number of available-for-sale debt securities in an unrealized loss position | security	150		150		46
U.S. government-sponsored enterprises debt securities
Unrealized Loss
Number of available-for-sale debt securities in an unrealized loss position | security	48		48
Corporate debt securities
Unrealized Loss
Number of available-for-sale debt securities in an unrealized loss position | security	22		22		17
AFS debt securities
Unrealized Loss
Excluded accrued interest receivables	$ 27,000,000		$ 27,000,000		$ 22,300,000