Commitments and Contingencies Outstanding Commitments to Extend Credit and Letters of Credit (Details) - Reserve for Off-balance Sheet Activities [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Valuation allowances and reserves, balance	$ 6,418,380	$ 6,205,029
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Valuation allowances and reserves, balance	318,827	326,973
Commercial Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Valuation allowances and reserves, balance	$ 43,709	$ 41,801