Outstanding Commitments to Extend Credit and Letters of Credit (Details) - Reserve for Off-balance Sheet Activities - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Valuation allowances and reserves	$ 414,258	$ 414,769
Commercial and other
Valuation allowances and reserves	3,518,960	2,972,105
Home equity
Valuation allowances and reserves	1,300,062	1,291,596
Commerical mortgage and construction
Valuation allowances and reserves	965,116	558,662
Total commitments to extend credit
Valuation allowances and reserves	5,784,138	4,822,363
Standby letters of credit
Valuation allowances and reserves	374,729	382,465
Commercial letters of credit
Valuation allowances and reserves	39,529	32,304
Residential Mortgage
Valuation allowances and reserves	$ 2,600	$ 3,200