Derivative Instruments - Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2020
Credit Derivatives [Line Items]
Derivative, Notional Amount	$ 11,729		$ 12,129
Fair Value	(33)		(61)
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount	783		784
Fair Value	18		18
Offsetting Notional Amount	108		109
Offsetting Fair Value	3		3
Credit derivatives \| Single name credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	100		175
Fair Value	$ 2		9
Weighted Average Years to Maturity	5 years	5 years
Offsetting Notional Amount	$ 0		0
Offsetting Fair Value	0		0
Credit derivatives \| Basket credit default swaps \| BBB Plus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	500		500
Fair Value	$ 12		12
Weighted Average Years to Maturity	5 years	5 years
Offsetting Notional Amount	$ 0		0
Offsetting Fair Value	0		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
Fair Value	$ 1
Weighted Average Years to Maturity	7 years
Offsetting Notional Amount	$ 100
Offsetting Fair Value	(1)
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, CCC Rating [Member] \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	8
Fair Value	$ (4)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year
Offsetting Notional Amount	$ 8
Offsetting Fair Value	4
Credit derivatives \| Basket credit default swaps \| A \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount			100
Fair Value			1
Average Term of Credit Risk Derivatives Less than 1 Year		8 years
Offsetting Notional Amount			100
Offsetting Fair Value			(1)
Credit derivatives \| Basket credit default swaps \| CCC Minus \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount			9
Fair Value			(4)
Average Term of Credit Risk Derivatives Less than 1 Year		Less than 1 year
Offsetting Notional Amount			9
Offsetting Fair Value			$ 4
Credit derivatives \| Credit derivatives that assume credit risk \| 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
Offsetting Fair Value	$ 0

Average Term of Credit Risk Derivatives Less than 1 Year

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- Definition

Derivative, Nominal Value, Amount Offset Against Collateral, Net

+ References

No definition available.

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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
-Publisher FASB
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- Definition

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

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
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-URI http://asc.fasb.org/extlink&oid=121590274&loc=d3e41678-113959

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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
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&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
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

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