Composition of loans held-in-portfolio-covered loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	$ 24,657,720	$ 24,951,299
Commercial Real Estate Construction Financing Receivable Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	651,554	786,765
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	7,129,273	6,691,414
Consumer Portfolio Segment Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	3,920,038	3,789,936
Covered Under Loss Sharing Agreements With F D I C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-in-portfolio	3,903,867	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	2,153,790	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	170,572	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	393,101	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	1,106,851	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	$ 79,553	$ 116,181