Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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
Total assets of partnerships in which the company invested	150,481,060,000		142,601,105,000
Investment in partnership carrying amount	853,000,000		861,000,000
Unfunded commitments includes carrrying amount of its investments	361,000,000		406,000,000
Maximum exposure to loss of investments in real estate partnerships	1,100,000,000
Investments amortized to income tax expense	19,000,000	$ 21,000,000
Federal tax credits and other federal tax benefits recognized	21,000,000	$ 26,000,000
Variable Interest Entity Primary Beneficiary [Member]
Total assets of partnerships in which the company invested	$ 2,300,000,000		$ 2,300,000,000