Variable Interest Entities and Asset Securitizations - Additional Information (Detail) (USD $)	3 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Residential mortgage loans securitized with Ginnie Mae	$ 923,000,000
Residential mortgage loans securitized formerly held in Company's portfolio	296,000,000
Residential mortgage loans securitized newly originated	627,000,000
Resulting securities retained	917,000,000
Recognized gain	7,000,000
Gains of newly originated loans	10,000,000
Amount of Loans guaranteed	1,000,000,000
Carrying value of loans in the Securitization trusts	133,000,000	151,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties	20,000,000	23,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts	34,000,000	34,000,000
Total assets of real estate partnerships in which the company invested	1,400,000,000	1,500,000,000
Maximum exposure to loss of investments in real estate partnerships	264,000,000	270,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	$ 75,000,000	$ 71,000,000