Fair Value of Financial Instruments - Summary of Fair Value Information of Financial Instruments (Parenthetical) (Detail) - Fair Value Measurements, Recurring [Member] - Mortgage Loans [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair value	$ 115	$ 115
Book value	$ 115	$ 115