Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Variable Interest Entity Disclosure [Abstract]
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		1,000,000,000
Maximum exposure to loss of investments in real estate partnerships	316,000,000		294,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	114,000,000		$ 102,000,000
Investments amortized to income tax expense	13,000,000	$ 11,000,000
Federal tax credits and other federal tax benefits recognized	$ 16,000,000	$ 14,000,000