Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	151,901,194,000		151,901,194,000		142,601,105,000
Investment in partnership carrying amount	858,000,000		858,000,000		861,000,000
Unfunded commitments includes carrrying amount of its investments	341,000,000		341,000,000		406,000,000
Maximum exposure to loss of investments in real estate partnerships	1,100,000,000		1,100,000,000
Investments amortized to income tax expense	25,000,000	$ 22,000,000	63,000,000	$ 65,000,000
Federal tax credits and other federal tax benefits recognized	27,000,000	$ 26,000,000	70,000,000	$ 78,000,000
Variable Interest Entity Primary Beneficiary [Member]
Total assets of partnerships in which the company invested	$ 2,900,000,000		$ 2,900,000,000		$ 2,300,000,000