Derivative Instruments - Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Derivative, Notional Amount	$ 12,063	$ 13,706
Fair Value	(58)	(66)
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount	712	515
Fair Value	3	8
Offsetting Notional Amount	112	15
Offsetting Fair Value	4	5
Credit derivatives \| Single name credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	100	100
Fair Value	$ 1	$ 3
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	400
Fair Value	$ 6	$ 10
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	$ 0
Weighted Average Years to Maturity	8 years
Offsetting Notional Amount	$ 100
Offsetting Fair Value	0
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, CCC Rating [Member] \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	12
Fair Value	$ (4)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year
Offsetting Notional Amount	$ 12
Offsetting Fair Value	$ 4
Credit derivatives \| Basket credit default swaps \| A \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		1
Fair Value		$ 0
Average Term of Credit Risk Derivatives Less than 1 Year		Less than 1 year
Offsetting Notional Amount		$ 1
Offsetting Fair Value		0
Credit derivatives \| Basket credit default swaps \| CCC Minus \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		14
Fair Value		$ (5)
Average Term of Credit Risk Derivatives Less than 1 Year		Less than 1 year
Offsetting Notional Amount		$ 14
Offsetting Fair Value		$ 5

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
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5708775-113959

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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
-Subparagraph (a)
-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

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

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