Investment Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Securities continuous unrealized loss position, fair value	$ 1,300,000,000	$ 1,700,000,000
Securities continuous unrealized loss position fair value (as percent)	36.60%	70.30%
Short-term investments, total	$ 163,700,000
Securities pledged as collateral	1,700,000,000	$ 1,000,000,000.0
Available-for-sale securities, gross realized losses	13,300,000	65,000	$ 2,400,000
Available-for-sale securities, gross realized losses	$ 4,000	$ 4,000	$ 1,300,000
Income tax benefit related to security gains (losses) (as percent)	26.135%	26.135%	39.225%
Bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, gross realized losses	$ 7,300,000
Bonds sold amount	$ 89,000,000