Outstanding Commitments to Extend Credit and Letters of Credit (Details) - Reserve for Off-balance Sheet Activities - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Valuation allowances and reserves	$ 395,260	$ 414,258
Commercial and other
Valuation allowances and reserves	3,673,815	3,518,960
Home equity
Valuation allowances and reserves	1,368,465	1,300,062
Commerical mortgage and construction
Valuation allowances and reserves	1,033,287	965,116
Total commitments to extend credit
Valuation allowances and reserves	6,075,567	5,784,138
Standby letters of credit
Valuation allowances and reserves	356,359	374,729
Commercial letters of credit
Valuation allowances and reserves	$ 38,901	$ 39,529