Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Variable Interest Entity Disclosure [Abstract]
Loss on securitization of assets	$ 0	$ 0
Other assets for its "investment" in the common securities recognized by the company of various trusts	23,000,000		$ 23,000,000
Total assets of partnerships in which the company invested	1,100,000,000		1,100,000,000
Maximum exposure to loss of investments in real estate partnerships		517,000,000	523,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships		278,000,000	$ 280,000,000
Investments amortized to income tax expense	17,000,000	13,000,000
Federal tax credits and other federal tax benefits recognized	$ 20,000,000	$ 16,000,000