Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity Disclosure [Abstract]
Carrying value of loans in the Securitization trusts		$ 81,000,000
Combined outstanding principal amount of mortgage-backed securities issued by qualified special purpose trust held by unrelated parties		13,000,000
Residential mortgage loans securitized with Ginnie Mae	$ 24,000,000	65,000,000	$ 135,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts	24,000,000	24,000,000
Total assets of partnerships in which the company invested	1,000,000,000	1,100,000,000
Maximum exposure to loss of investments in real estate partnerships	294,000,000	295,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	$ 102,000,000	$ 78,000,000