Securities - Narrative (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) security contract	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
Carrying value of securities pledged to secure public deposits, derivatives and other secured borrowings			$ 903,000,000	$ 918,000,000
Number of available-for-sale debt securities in unrealized loss position | contract			57
Number of held-to-maturity debt securities in unrealized loss position | security			4
Other-than-temporary impairment charges	$ 0	$ 0
Allowance for credit losses, held-to-maturity portfolio			$ 0
Allowance for credit losses, available-for-sale portfolio			$ 0