Securities (Narrative) (Details)	6 Months Ended
	Jun. 30, 2020 USD ($) Security	Jun. 30, 2019 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investments Debt And Equity Securities [Abstract]
Amortized cost of securities excluding accrued interest	$ 23,500,000			$ 23,900,000
Securities classified as trading	0			0
Proceeds from sales of securities	124,100,000	$ 0
Gross gains	1,100,000
Gross losses	1,000,000.0
Securities pledged as collateral	3,300,000,000			$ 3,300,000,000
Allowance for credit loss	$ 0		$ 0
Securities that met the criteria of a credit loss event | Security	0