Income Taxes (Details 3)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective income tax rate reconciliation
Statutory rate (as a percent)	35.00%	35.00%	35.00%
Net state income tax (as a percent)	6.40%	6.00%	6.10%
Tax exempt income (as a percent)	(4.50%)	(4.60%)	(4.20%)
Affordable housing investments (as a percent)	(5.50%)	(4.90%)	(4.70%)
All other, net (as a percent)	0.20%	(2.60%)	(0.10%)
Effective tax provision (benefit) (as a percent)	31.60%	28.90%	32.10%