Loans - Additional Information (Detail) (USD $)	3 Months Ended						3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Government National Mortgage Association Certificates And Obligations GNMA Member	Mar. 31, 2011 Government National Mortgage Association Certificates And Obligations GNMA Member	Mar. 31, 2012 Federal National Mortgage Association Certificates And Obligations FNMA Member	Mar. 31, 2011 Federal National Mortgage Association Certificates And Obligations FNMA Member	Mar. 31, 2012 Residential Mortgage	Mar. 31, 2011 Residential Mortgage	Mar. 31, 2012 Mortgages	Mar. 31, 2011 Mortgages	Mar. 31, 2012 Construction Loans [Member]	Mar. 31, 2011 Construction Loans [Member]	Mar. 31, 2011 Commercial Loans [Member]	Mar. 31, 2012 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Dec. 31, 2011 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Mar. 31, 2012 Westernbank Puerto Rico [Member] Covered Under Loss Sharing Agreements With F D I C [Member] A S C Subtopic 31030 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Dec. 31, 2011 Westernbank Puerto Rico [Member] Covered Under Loss Sharing Agreements With F D I C [Member] A S C Subtopic 31030 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Acquired With Deteriorated Credit Quality														$ 300,000,000	$ 300,000,000
Outstanding principal balance of covered loans																5,800,000,000	6,000,000,000
Purchase of Loans	0								215,000,000	439,000,000	1,000,000	0	0
Residential Mortgage Loans Sold							50,000,000	235,000,000
Loan Securitization			190,000,000	256,000,000	60,000,000	73,000,000
Commercial Construction Loans Sold	$ 20,000,000	$ 2,000,000