Loans, Allowance for Loan and Lease Losses, and Reserve for Off-Balance Sheet Credit Commitments (Detail 2) - Credit Risk	9 Months Ended
	Sep. 30, 2015 item
Acquired impaired loans
Concentrations of credit risk
Number of states with largest concentration by loan type	5
Total loans outstanding | Excluding acquired impaired loans | California
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	72.00%
Total loans outstanding | Excluding acquired impaired loans | New York
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	10.00%
Total loans outstanding | Excluding acquired impaired loans | Other states and countries
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	18.00%
Total loans outstanding | Acquired impaired loans | California
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	29.00%
Total loans outstanding | Acquired impaired loans | Texas
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	12.00%
Total loans outstanding | Acquired impaired loans | Nevada
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	6.00%
Total loans outstanding | Acquired impaired loans | Ohio
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	6.00%
Total loans outstanding | Acquired impaired loans | Arizona
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	6.00%
Total loans outstanding | Acquired impaired loans | Other states
Concentrations of credit risk
Percent of total loans outstanding (as a percent)	41.00%