Securities (Narrative) (Details)	Mar. 31, 2021 USD ($) Security	Dec. 31, 2020 USD ($) Security
Investments Debt And Equity Securities [Abstract]
Amortized cost of securities excluding accrued interest	$ 24,400,000	$ 24,400,000
Securities classified as trading	0	0
Securities pledged as collateral	3,000,000,000.0	$ 3,400,000,000
Allowance for credit loss	$ 0
Securities that met the criteria of a credit loss event | Security	0
Number of securities with market values below their cost basis | Security	105	28