Securities (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investment Security Gains, net (Note)	$ 2,400,000	$ 400,000	$ 2,100,000	$ 300,000
Gross proceeds from sale of securities	$ 10,000,000	4,500,000	523,600,000	106,500,000
Gross realized securities gains			$ 300,000	100,000
Gross realized securities losses				400,000
Number of securities in an unrealized loss position | Investment	507		507
Total fair value	$ 10,964,900,000		$ 10,964,900,000		$ 23,548,600,000
Total unrealized losses	73,900,000		73,900,000		$ 140,500,000
Net impairment losses recognized in earnings	2,400,000	$ 0	2,400,000	$ 0
Government Sponsored Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	24,200,000		24,200,000
Corporate Debt
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 11,100,000		$ 11,100,000
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	$ 29,500,000		$ 29,500,000
Auction Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total unrealized losses	$ 200,000		$ 200,000