Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity Disclosure [Abstract]
Residential mortgage loans securitized with Ginnie Mae	$ 65,000,000	$ 135,000,000	$ 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	81,000,000	98,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties	13,000,000	15,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts	24,000,000	34,000,000
Total assets of partnerships in which the company invested	1,100,000,000	1,200,000,000
Maximum exposure to loss of investments in real estate partnerships	295,000,000	243,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	78,000,000	56,000,000
Investments amortized to income tax expense	46,531,000	53,383,000	48,019,000
Federal tax credits and other federal tax benefits recognized	$ 62,000,000	$ 68,000,000	$ 66,000,000