Trust Preferred Securities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011
Debt Disclosure [Line Items]
Number of statutory trusts	5
Maximum percentage of restricted core capital elements to all core capital elements that may be included in the Tier 1 capital	25.00%
Trust preferred securities, amount subject to the Dodd-Frank Act	$ 427
Trust preferred securities, amount not subject to the Dodd-Frank Act	$ 935