Commitments and contingencies - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended					9 Months Ended			1 Months Ended
	Sep. 30, 2014 D		Sep. 30, 2013	Sep. 30, 2014 D		Sep. 30, 2013	Dec. 31, 2013		Sep. 30, 2014 Pending Litigation Against Multiple Defendants [Member]	Sep. 30, 2014 Minimum Member	Sep. 30, 2014 Maximum Member	Oct. 31, 2014 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Oct. 30, 2014 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Sep. 30, 2014 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Sep. 30, 2014 Credit Concentration Risk Member Government PR Government Indirect Exposure [Member] Housing Bonds backed by GNMA, FNMA or residential CMOs	Dec. 31, 2013 Credit Concentration Risk Member Government PR Government Indirect Exposure [Member] Housing Bonds backed by GNMA, FNMA or residential CMOs	Sep. 30, 2014 Credit Concentration Risk Member Government PR Government Indirect Exposure [Member] Long-term Debt [Member]	Dec. 31, 2013 Credit Concentration Risk Member Government PR Government Indirect Exposure [Member] Long-term Debt [Member]	Sep. 30, 2014 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member]	Dec. 31, 2013 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member]	Sep. 30, 2014 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member] From PR Government And Public Corporations [Member]	Dec. 31, 2013 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member] From PR Government And Public Corporations [Member]	Sep. 30, 2014 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member] From Municipalities [Member]	Dec. 31, 2013 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Direct Exposure [Member] From Municipalities [Member]	Sep. 30, 2014 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Indirect Exposure [Member]	Dec. 31, 2013 Credit Concentration Risk Member Outstanding Balance [Member] Government PR Government Indirect Exposure [Member]	Sep. 30, 2014 Credit Concentration Risk Member Total [Member] Government PR Government Direct Exposure [Member]	Dec. 31, 2013 Credit Concentration Risk Member Total [Member] Government PR Government Direct Exposure [Member]	Sep. 30, 2014 Credit Concentration Risk Member Total [Member] Government PR Government Indirect Exposure [Member]	Dec. 31, 2013 Credit Concentration Risk Member Total [Member] Government PR Government Indirect Exposure [Member]	Sep. 30, 2014 Commitments To Extend Credit Member	Dec. 31, 2013 Commitments To Extend Credit Member
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments																															$ 13,000,000	$ 7,000,000
Unrecorded Unconditional Purchase Obligation Balance Sheet Amount	10,000,000			10,000,000			10,000,000
Estimate of possible loss	126,000,000			126,000,000			128,000,000
Concentration Of Risk Credit Facilities															49,000,000	52,000,000	32,000,000	34,000,000	727,000,000	950,000,000	257,000,000	527,000,000	470,000,000	423,000,000			823,000,000	1,200,000,000	362,000,000	360,000,000
True Up Payment Term	45			45
Loss Contingency Range Of Possible Loss Portion Not Accrued										0	56,500,000
Loans and Leases Receivable, Consumer, Mortgage with PRHA																									281,000,000	274,000,000
F D I C Indemnification Asset Cash Payments Received	(73,106,000)		(52,865,000)	(185,963,000)		(52,758,000)						74,100,000
Total Unreimbursed F D I C Shared Loss Claims												273,900,000		348,000,000
Loans And Leases Receivable Net Of Deferred Income	19,359,216,000	[1]		19,359,216,000	[1]		21,611,866,000	[1]											592,000,000	789,000,000
Investments																			135,000,000	161,000,000
Loss Contingency Aggregate Claims Damages Sought									98,000,000
Loss Contingency Claim Damages Sought									60,000,000
Unreimbursed Claims Submitted to the FDIC													184,000,000
Unreimbursed Claims Yet To Be Submitted To The FDIC													$ 89,900,000

[1] Non-covered loans held-in-portfolio at September 30, 2014 are net of $91 million in unearned income and exclude $178 million in loans held-for-sale. (December 31, 2013 - $92 million in unearned income and $110 million in loans held-for-sale.)