Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss on securitization of assets	$ 0	$ 0	$ 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	142,601,105,000	119,872,757,000
Investment in partnership carrying amount	861,000,000	748,000,000
Unfunded commitments includes carrrying amount of its investments	406,000,000	414,000,000
Maximum exposure to loss of investments in real estate partnerships	1,200,000
Variable Interest Entity Primary Beneficiary [Member]
Total assets of partnerships in which the company invested	$ 2,300,000,000	$ 1,500,000,000