Commitments and contingencies - Additional Information (Detail) (USD $)															9 Months Ended	12 Months Ended
	Sep. 30, 2012 days	Dec. 31, 2011	Sep. 30, 2012 Minimum Member	Sep. 30, 2012 Maximum Member	Sep. 30, 2012 Credit Concentration Risk Member Foreign Government Debt Securities Member	Dec. 31, 2011 Credit Concentration Risk Member Foreign Government Debt Securities Member	Sep. 30, 2012 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Dec. 31, 2011 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Sep. 30, 2012 Credit Concentration Risk Member Other Credit Facilities [Member]	Dec. 31, 2011 Credit Concentration Risk Member Other Credit Facilities [Member]	Sep. 30, 2012 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Dec. 31, 2011 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Sep. 30, 2012 Commitments To Extend Credit Member Reserve For Off Balance Sheet Activities [Member] Line Of Credit Member	Dec. 31, 2011 Commitments To Extend Credit Member Reserve For Off Balance Sheet Activities [Member] Line Of Credit Member	Sep. 30, 2012 Putative Class Action [Member] Parent Company [Member]	Dec. 31, 2010 Securities Class Action [Member] Banco Popular De Puerto Rico [Member]
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments													$ 7,000,000	$ 15,000,000
Unrecorded Unconditional Purchase Obligation Balance Sheet Amount	10,000,000	10,000,000
Estimate of possible loss	103,000,000	98,000,000
Fair Value Concentration Of Risk Loans Receivable					145,000,000	154,000,000	12,800,000,000	12,500,000,000	777,000,000	1,200,000,000	215,000,000	140,000,000
Concentration Risk Percentage							62.00%	61.00%
Fair Value Concentration Of Risk Credit Facilities Granted									1,500,000,000	1,300,000,000
True Up Payment Term	45
Loss Contingency Range Of Possible Loss Portion Not Accrued			0	16,900,000
Loss Contingency Damages Sought Value																600,000,000
Litigation Settlement, Gross															$ 400,000