Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) Investment	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investment Security Gains, net (Note)	$ 300,000	$ 100,000
Gross proceeds from sale of securities	$ 513,600,000	$ 102,000,000
Number of securities in an unrealized loss position | Investment	644
Total fair value	$ 13,381,700,000		$ 23,548,600,000
Total unrealized losses	94,300,000		$ 140,500,000
Net impairment losses recognized in earnings	0
Government Sponsored Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	30,100,000
Corporate Debt
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 17,800,000
Percent of corporate debt portfolio	33.00%
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	$ 500,000