Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 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		$ 23,000,000
Total assets of partnerships in which the company invested	1,400,000,000		1,400,000,000		1,100,000,000
Maximum exposure to loss of investments in real estate partnerships	803,000,000		803,000,000
Investment in partnership carrying amount	604,000,000		604,000,000		523,000,000
Unfunded commitments includes carrrying amount of its investments	390,000,000		390,000,000		$ 280,000,000
Investments amortized to income tax expense	17,000,000	$ 13,000,000	51,000,000	39,000,000
Federal tax credits and other federal tax benefits recognized	21,000,000	$ 15,000,000	62,000,000	$ 47,000,000
Material losses related to involvement with partnership entities	$ 0		$ 0