Loans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2013 Sale Non Performing Loans [Member]	Mar. 31, 2013 Sale Non Performing Loans [Member]	Sep. 30, 2014 Residential Mortgage	Sep. 30, 2013 Residential Mortgage	Sep. 30, 2014 Residential Mortgage	Sep. 30, 2013 Residential Mortgage	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2014 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2014 Bulk Sale Bpna [Member]	Sep. 30, 2014 Consumer [Member]	Sep. 30, 2013 Consumer [Member]	Sep. 30, 2014 Consumer [Member]	Sep. 30, 2013 Consumer [Member]	Sep. 30, 2014 Mortgages [Member]	Sep. 30, 2013 Mortgages [Member]	Sep. 30, 2014 Mortgages [Member]	Sep. 30, 2013 Mortgages [Member]	Sep. 30, 2014 Commercial Loans [Member]	Sep. 30, 2013 Commercial Loans [Member]	Sep. 30, 2014 Commercial Loans [Member]	Sep. 30, 2013 Commercial Loans [Member]	Sep. 30, 2014 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Sep. 30, 2013 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Sep. 30, 2014 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, 2013 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]	Sep. 30, 2014 SOP Non-Covered Loans [Member] A S C Subtopic 31030 [Member]	Dec. 31, 2013 SOP Non-Covered Loans [Member] A S C Subtopic 31030 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Acquired With Deteriorated Credit Quality																																								$ 100,000,000	$ 200,000,000
Outstanding principal balance of SOP loans																																										3,200,000,000	3,800,000,000	236,000,000	197,000,000
Purchase of Loans																												0	0	92,000,000	42,000,000	139,000,000	199,000,000	470,000,000	1,700,000,000	0	5,000,000	21,000,000	8,000,000
Residential Mortgage Loans Sold					435,000,000		56,000,000	60,000,000	126,000,000	614,000,000
Commercial Construction Loans Sold	96,000,000	6,000,000	157,000,000	413,000,000		401,000,000
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds							225,236,000	307,339,000	704,244,000	1,163,045,000	222,525,000	302,873,000	695,416,000	1,149,199,000	171,508,000	199,824,000	521,747,000	767,393,000	51,017,000	101,922,000	173,669,000	353,987,000	0	1,127,000	0	27,819,000
Financing Receivable Reclassification To Held For Sale																											105,000,000
Loans Sold																											$ 115,700,000