Special Purpose Entities, Including Variable Interest Entities - Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Fixed income securities, at fair value (amortized cost of $2,480,532 and $3,020,744)	$ 3,038	$ 3,187
Investments:
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	81	132
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	81	5
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Investments:
Loans Unpaid Principal Balance	2,439	2,618
Long Term Debt Unpaid Principal Balance	3,550	3,800
Municipal Bonds [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Fixed income securities, at fair value (amortized cost of $2,480,532 and $3,020,744)	116	139
Investments:
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	$ 6	$ 25