Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	1,100,000,000		1,100,000,000		1,100,000,000
Maximum exposure to loss of investments in real estate partnerships	573,000,000		573,000,000		523,000,000
Unfunded commitments included in company's maximum exposure to loss of investments in real estate partnerships	267,000,000		267,000,000		$ 280,000,000
Investments amortized to income tax expense	17,000,000	$ 13,000,000	34,000,000	26,000,000
Federal tax credits and other federal tax benefits recognized	21,000,000	$ 16,000,000	41,000,000	$ 32,000,000
Material losses related to involvement with partnership entities	$ 0		$ 0