Variable Interest Entities (Detail)	3 Months Ended
	Mar. 31, 2012
Core CDO Holdings Portfolio [Member]
Variable Interest Entity Not Primary Beneficiary Aggregated Disclosure	the Company has not been involved in establishing these entities and is not the primary beneficiary of these VIEs as contemplated in current authoritative accounting guidance.
Financial Guarantee and Credit Default Swap Contracts [Member]
Variable Interest Entity Not Primary Beneficiary Aggregated Disclosure	The Company has a limited number of remaining outstanding credit enhancement exposures, including written financial guarantee and credit default swap contracts. The obligations related to these transactions are often securitized through VIEs. The Company is not the primary beneficiary of these VIEs as contemplated in current authoritative accounting guidance on the basis that management does not believe that the Company has the power to direct the activities, such as asset selection and collateral management, which most significantly impact each entity's economic performance.