Investments - Summary of Aggregate Contractual or Notional Amounts and Estimated Fair Values Related to Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Embedded Derivative on Funds Withheld Liability [Member]
Derivative [Line Items]
Contractual/Notional Amount	$ 182	$ 172
Estimated Fair Value, Asset		4
With Hedge Designation [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual/Notional Amount	715	500
Estimated Fair Value, Asset		11
Estimated Fair Value, (Liability)	(8)
Without Hedge Designation [Member] \| Equity Markets, Options - Purchased [Member]
Derivative [Line Items]
Contractual/Notional Amount	57	213
Estimated Fair Value, Asset	1	18
Without Hedge Designation [Member] \| Equity Markets, Options - Written [Member]
Derivative [Line Items]
Contractual/Notional Amount	100	239
Estimated Fair Value, (Liability)	(1)	(17)
Without Hedge Designation [Member] \| Commodity Futures [Member] \| Long [Member]
Derivative [Line Items]
Contractual/Notional Amount		$ 32
Without Hedge Designation [Member] \| Embedded Derivative on Funds Withheld Liability [Member]
Derivative [Line Items]
Estimated Fair Value, (Liability)	$ (7)

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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