Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) Investment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investment Security Gains, net	$ 300,000	$ (300,000)
Other Than Temporary Impairment Losses	100,000	0
Gross proceeds from sale of securities	541,300,000	513,600,000
Gross realized securities losses	$ 200,000
Gross realized securities gains		300,000
Number of securities in an unrealized loss position | Investment	1,074
Total fair value	$ 19,997,500,000		$ 22,040,200,000
Total unrealized losses	152,800,000		$ 176,000,000
Net impairment losses recognized in earnings		$ 0
Government Sponsored Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	63,600,000
Corporate Debt
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 23,000,000
Percent of corporate debt portfolio	35.00%
Other | Community Reinvestment Act CRA
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 34,000,000
Auction Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 300,000