Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Derivative, Notional Amount	$ 11,425	$ 12,129
Fair Value	(36)	(61)
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount	181	784
Fair Value	5	18
Offsetting Notional Amount	106	109
Derivative, Fair Value, Gross Offsetting Amount	2	3
Credit derivatives \| Single name credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		175
Fair Value		$ 9
Weighted Average Years to Maturity		5 years
Offsetting Notional Amount		$ 0
Derivative, Fair Value, Gross Offsetting Amount		0
Credit derivatives \| Basket credit default swaps \| BBB Plus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		500
Fair Value		$ 12
Weighted Average Years to Maturity		5 years
Offsetting Notional Amount		$ 0
Derivative, Fair Value, Gross Offsetting Amount		0
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, AAA Rating [Member] \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	100	100
Fair Value	$ 1	$ 1
Weighted Average Years to Maturity	7 years	8 years
Offsetting Notional Amount	$ 100	$ 100
Derivative, Fair Value, Gross Offsetting Amount	(1)	(1)
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, B+ Rating \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	75
Fair Value	$ 7
Weighted Average Years to Maturity	5 years
Offsetting Notional Amount	$ 0
Derivative, Fair Value, Gross Offsetting Amount	0
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, CCC+ Rating \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	6	9
Fair Value	$ (3)	$ (4)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year	Less than 1 year
Offsetting Notional Amount	$ 6	$ 9
Derivative, Fair Value, Gross Offsetting Amount	$ 3	$ 4

Average Term of Credit Risk Derivatives Less than 1 Year

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Derivative, Fair Value, Gross Offsetting Amount

+ References

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Derivative, Nominal Value, Gross Offsetting Amount

+ References

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- Definition

Average period covered by credit risk derivative contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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