Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Loss on securitization of assets			$ 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	150,622,707,000		150,622,707,000		142,601,105,000
Investment in partnership carrying amount	868,000,000		868,000,000		861,000,000
Unfunded commitments includes carrrying amount of its investments	350,000,000		350,000,000		406,000,000
Maximum exposure to loss of investments in real estate partnerships	1,200,000,000		1,200,000,000
Investments amortized to income tax expense	19,000,000	$ 22,000,000	38,000,000	$ 43,000,000
Federal tax credits and other federal tax benefits recognized	22,000,000	$ 26,000,000	43,000,000	$ 52,000,000
Variable Interest Entity Primary Beneficiary [Member]
Total assets of partnerships in which the company invested	$ 2,500,000,000		$ 2,500,000,000		$ 2,300,000,000