Variable Interest Entities and Asset Securitizations - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity Disclosure [Abstract]
Residential mortgage loans securitized with Ginnie Mae	$ 133,000,000	$ 3,000,000,000
Residential mortgage loans securitized formerly held in Company's portfolio		1,300,000,000
Recognized gain		42,000,000
Gains of newly originated loans		28,000,000
Automobile loans securitized and sold	0	1,400,000,000
Recognized gain sale of securities		20,683,000
Carrying value of loans in the Securitization trusts	98,000,000	121,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties	15,000,000	18,000,000
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	1,200,000,000	1,300,000,000
Maximum exposure to loss of investments in real estate partnerships	243,000,000	236,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	$ 56,000,000	$ 45,000,000