Composition of loans held-in-portfolio-covered loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	$ 19,082,387	$ 24,951,299	$ 25,406,339
Commercial Real Estate Construction Financing Receivable Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio		786,765	911,070
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio		6,691,414	6,143,158
Consumer Portfolio Segment Member
Accounts, Notes, Loans and Financing Receivable [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]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	4,221,788	4,348,703
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
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]
Accounts, Notes, Loans and Financing Receivable [Line Items]
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
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	532,433	546,826
Covered Under Loss Sharing Agreements With F D I C [Member] | Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
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
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	$ 106,658	$ 116,181	$ 151,757