Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	$ 19,082,387	$ 24,951,299	$ 25,406,339
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio		786,765	911,070
Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio		6,691,414	6,143,158
Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	3,741,578	3,789,936	3,777,043
Covered Under Loss Sharing Agreements With F D I C [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	125,199	76,005
Financing Receivable Recorded Investment 60 To 89 Days Past Due	34,354	58,815
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	1,249,587	1,265,530
Total Past Due	1,409,140	1,400,350
Financing Receivable Recorded Investment Current	2,812,648	2,948,353
Loans held-in-portfolio	4,221,788	4,348,703
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	53,879	35,286
Financing Receivable Recorded Investment 60 To 89 Days Past Due	20,695	25,273
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	537,549	519,222
Total Past Due	612,123	579,781
Financing Receivable Recorded Investment Current	1,590,737	1,691,514
Loans held-in-portfolio	2,202,860	2,271,295
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	5,483	4,438
Financing Receivable Recorded Investment 60 To 89 Days Past Due	4,708	1,390
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	93,658	99,555
Total Past Due	103,849	105,383
Financing Receivable Recorded Investment Current	124,992	136,064
Loans held-in-portfolio	228,841	241,447
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	2,411	997
Financing Receivable Recorded Investment 60 To 89 Days Past Due	480	625
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	415,960	434,661
Total Past Due	418,851	436,283
Financing Receivable Recorded Investment Current	113,582	110,543
Loans held-in-portfolio	532,433	546,826
Covered Under Loss Sharing Agreements With F D I C [Member] | Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	58,408	32,371
Financing Receivable Recorded Investment 60 To 89 Days Past Due	6,532	28,238
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	187,719	196,541
Total Past Due	252,659	257,150
Financing Receivable Recorded Investment Current	898,337	915,804
Loans held-in-portfolio	1,150,996	1,172,954
Covered Under Loss Sharing Agreements With F D I C [Member] | Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	5,018	2,913
Financing Receivable Recorded Investment 60 To 89 Days Past Due	1,939	3,289
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	14,701	15,551
Total Past Due	21,658	21,753
Financing Receivable Recorded Investment Current	85,000	94,428
Loans held-in-portfolio	$ 106,658	$ 116,181	$ 151,757