Variable Interest Entities and Asset Securitizations - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Variable Interest Entity Disclosure [Abstract]
Residential mortgage loans securitized with Ginnie Mae	$ 1,800,000,000	$ 2,800,000,000
Residential mortgage loans securitized formerly held in Company's portfolio	1,000,000,000	1,400,000,000
Residential mortgage loans securitized newly originated	811,000,000	1,400,000,000
Recognized gain	35,000,000	42,000,000
Gains of newly originated loans	15,000,000	25,000,000
Automobile loans securitized and sold	1,400,000,000
Recognized gains sale of securities	21,000,000
Carrying value of loans in the Securitization trusts	126,000,000	126,000,000	151,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties	19,000,000	19,000,000	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	34,000,000
Total assets of real estate partnerships in which the company invested	1,400,000,000	1,400,000,000	1,500,000,000
Maximum exposure to loss of investments in real estate partnerships	250,000,000	250,000,000	270,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	$ 57,000,000	$ 57,000,000	$ 71,000,000