Investment Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Securities continuous unrealized loss position, fair value	$ 1,700,000,000	$ 1,400,000,000
Securities continuous unrealized loss position fair value (as percent)	70.30%	73.50%
Securities pledged as collateral	$ 1,000,000,000	$ 1,200,000,000
Available-for-sale securities, gross realized losses	65,000	2,400,000	$ 5,800,000
Available-for-sale securities, gross realized losses	$ 4,000	$ 1,300,000	$ 0
Income tax benefit related to security gains (losses) (as percent)	26.135%	39.225%	39.225%