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Investments - Summary of Aggregate Contractual or Notional Amounts and Estimated Fair Values Related to Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Embedded Derivative on Funds Withheld Liability [Member]
Derivative [Line Items]
Contractual/Notional Amount	$ 174	$ 172
Estimated Fair Value, Asset		4
Estimated Fair Value, (Liability)	(2)
With Hedge Designation [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual/Notional Amount	540	500
Estimated Fair Value, Asset	3	11
Estimated Fair Value, (Liability)	(1)
Without Hedge Designation [Member] | Equity Markets, Options - Purchased [Member]
Derivative [Line Items]
Contractual/Notional Amount	353	213
Estimated Fair Value, Asset	7	18
Without Hedge Designation [Member] | Equity Markets, Options - Written [Member]
Derivative [Line Items]
Contractual/Notional Amount	127	239
Estimated Fair Value, (Liability)	(6)	(17)
Without Hedge Designation [Member] | Equity Futures [Member] | Short [Member]
Derivative [Line Items]
Contractual/Notional Amount	50
Without Hedge Designation [Member] | Commodity Futures [Member] | Long [Member]
Derivative [Line Items]
Contractual/Notional Amount	$ 12	$ 32

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 860
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-Section 50
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
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+ References

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No definition available.

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