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Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 0	$ 3
Investment expense	(1)	(1)	$ (4)	$ (4)
Securities available-for-sale and short-term	15	24	59	80
Net investment income	21	37	112	69
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			16	(12)
Other Investments Income	(1)	3	14	7
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	16	24	63	79
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	0	1	0	4
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ 6	$ 14	$ 53	$ (11)

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Other Investments Income

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Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
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Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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