Commitments and contingencies - Additional Information (Detail) (USD $)											6 Months Ended	12 Months Ended
	Jun. 30, 2013 D	Dec. 31, 2012	Jun. 30, 2013 Minimum Member	Jun. 30, 2013 Maximum Member	Jun. 30, 2013 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Jun. 30, 2012 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Jun. 30, 2013 Credit Concentration Risk Member Outstanding Balance [Member]	Dec. 31, 2012 Credit Concentration Risk Member Outstanding Balance [Member]	Jun. 30, 2013 Credit Concentration Risk Member Foreign Government Debt Securities Member	Dec. 31, 2012 Credit Concentration Risk Member Foreign Government Debt Securities Member	Jun. 30, 2013 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Dec. 31, 2012 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Jun. 30, 2013 Credit Concentration Risk Member Other Credit Facilities [Member]	Dec. 31, 2012 Credit Concentration Risk Member Other Credit Facilities [Member]	Jun. 30, 2013 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Dec. 31, 2012 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Jun. 30, 2013 Credit Concentration Risk Member Uncommitted Credit Facility [Member] Outstanding Balance [Member]	Dec. 31, 2012 Credit Concentration Risk Member Uncommitted Credit Facility [Member] Outstanding Balance [Member]	Jun. 30, 2013 Commitments To Extend Credit Member	Dec. 31, 2012 Commitments To Extend Credit Member
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments																			$ 5,000,000	$ 5,000,000
Unrecorded Unconditional Purchase Obligation Balance Sheet Amount	10,000,000	10,000,000
Estimate of possible loss	119,000,000	112,000,000
Fair Value Concentration Of Risk Loans Receivable									201,000,000	217,000,000	14,300,000,000	13,300,000,000			215,000,000	75,000,000	2,200,000	61,000,000
Concentration Risk Percentage											66.00%	64.00%
Fair Value Concentration Of Risk Credit Facilities Granted							623,000,000	681,000,000					900,000,000	800,000,000
True Up Payment Term	45
Loss Contingency Range Of Possible Loss Portion Not Accrued			0	12,400,000
Loans and Leases Receivable, Consumer, Mortgage with PRHA							259,000,000	294,000,000
Unreimbursed Claims Late Stage Real State Collateral Dependent Loans					287,100,000	71,100,000
Total Unreimbursed F D I C Shared Loss Claims					451,100,000
Methodology Computation Charge Offs					$ 102,600,000	$ 26,200,000