Securities (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) Investment	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Investment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities, transferred from available for sale	$ 160,800,000	$ 287,900,000	$ 160,800,000	$ 287,900,000
Investment security losses, net	(400,000)	(100,000)	(900,000)	(300,000)
Gross proceeds from sale of securities	177,300,000	0	406,600,000	178,600,000
Sale of investment securities realized gain	100,000		1,600,000	1,500,000
Sale of investment securities realized loss	$ 400,000		$ 2,200,000	1,500,000
Number of securities in an unrealized loss position | Investment	1,101		1,101
Total fair value	$ 21,200,000,000		$ 21,200,000,000
Total unrealized losses	154,900,000		154,900,000
Debt securities, unrealized losses	154,900,000		154,900,000		$ 357,100,000
OTTI losses	100,000	100,000	300,000	300,000
CRA Eligible, Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Investment security losses, net	100,000		300,000
OTTI losses	100,000	$ (100,000.0)	300,000	$ (300,000.0)
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	55,800,000		55,800,000
Debt securities, unrealized losses	55,800,000		55,800,000		150,500,000
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	4,600,000		4,600,000
Debt securities, unrealized losses	$ 4,600,000		$ 4,600,000		22,900,000
Percent of corporate debt portfolio	28.00%		28.00%
Other
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	$ 76,000,000.0		$ 76,000,000.0
Debt securities, unrealized losses	$ 76,000,000.0		$ 76,000,000.0		$ 69,600,000