Mortgage Banking Activities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Entity	Jun. 30, 2012
Mortgage Servicing Rights [Line Items]
Residential loans transferred to securitization entities	$ 1,800,000,000		$ 4,040,000,000
MSRs at a taxable REIT subsidiary	16,000,000		29,000,000
Mortgage Servicing Rights
Mortgage Servicing Rights [Line Items]
MSRs at a taxable REIT subsidiary	16,148,000	1,029,000	28,614,000	2,608,000
Number of securitization entities to which asset transferred			8
Rights acquired and retained to service, original loans transferred	1,780,000,000		3,340,000,000
Principal balance of residential loans for which servicing rights owned	$ 4,130,000,000		$ 4,130,000,000