Securities (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) Investment	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) Investment	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investment Security Gains, net	$ (200,000)	$ 0	$ 1,900,000	$ 300,000
Other Than Temporary Impairment Losses	0	0	2,400,000	0
Gross proceeds from sale of securities	$ 217,200,000	3,800,000	740,800,000	110,300,000
Gross realized securities gains			$ 500,000	100,000
Gross realized securities losses				400,000
Number of securities in an unrealized loss position | Investment	762		762
Total fair value	$ 13,764,300,000		$ 13,764,300,000		$ 23,548,600,000
Total unrealized losses	74,100,000		74,100,000		$ 140,500,000
Net impairment losses recognized in earnings	0	$ 0		$ 0
Government Sponsored Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	22,900,000		22,900,000
Corporate Debt
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 12,900,000		$ 12,900,000
Percent of corporate debt portfolio	31.00%		31.00%
Other | Community Reinvestment Act CRA
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 30,500,000		$ 30,500,000
Auction Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 300,000		$ 300,000