Securities - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
Carrying value of securities pledged to secure public deposits, derivatives and other secured borrowings		$ 559,000,000	$ 918,000,000
Number of available-for-sale securities in unrealized loss position | security		58
Number of held-to-maturity securities in unrealized loss position | security		6
Other-than-temporary impairment charges	$ 0
Allowance for credit losses, held-to-maturity portfolio		$ 0
Allowance for credit losses, available-for-sale portfolio		$ 0