Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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		$ 24,000,000
Total assets of partnerships in which the company invested	1,100,000,000		1,100,000,000		1,000,000,000
Maximum exposure to loss of investments in real estate partnerships	331,000,000		331,000,000		294,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	122,000,000		122,000,000		$ 102,000,000
Investments amortized to income tax expense	11,000,000	$ 11,000,000	24,000,000	$ 22,000,000
Federal tax credits and other federal tax benefits recognized	$ 15,000,000	$ 14,000,000	$ 31,000,000	$ 28,000,000