Variable Interest Entities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	119,872,757,000	120,097,403,000
Investment in partnership carrying amount	748,000,000	523,000,000
Unfunded commitments includes carrrying amount of its investments	414,000,000	280,000,000
Maximum exposure to loss of investments in real estate partnerships	984,000,000
Variable Interest Entity Primary Beneficiary [Member]
Total assets of partnerships in which the company invested	$ 1,500,000,000	$ 1,100,000,000