Commitments, Contingencies and Guarantees - Commitments (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Potential losses from standby letters of credit	$ 0	$ 0
Undisbursed loan commitments	606,700,000	578,200,000
Probable credit losses	1,100,000	1,300,000
Financial and Performance Standby Letters of Credit
Loss Contingencies [Line Items]
Letters of credit outstanding	139,000,000	118,900,000
Commitments to Extend Credit
Loss Contingencies [Line Items]
Loan commitments under financial guarantee	$ 2,930,000,000	$ 2,700,000,000