Fair Value of Financial Instruments - Summary of Fair Value Information of Financial Instruments (Parenthetical) (Detail) - Fair Value Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Mortgage Loans [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair value	$ 115	$ 115
Book value	115	115
Acquisition Loan [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair value	205	205
Book value	$ 205	$ 205

Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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Name:	us-gaap_InvestmentOwnedAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant