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Derivative Instruments (Exposure from Credit Derivatives by Rating of the Underlying Credits) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 13 | $ 5
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 1,517 | $ 1,306
Derivative Average Remaining Maturity | [1],[3] | 5 years 7 months 6 days | 3 years 8 months 12 days
Standard Poors AAA To A Ratings [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 11 | $ 2
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 287 | $ 142
Derivative Average Remaining Maturity | [1],[3] | 15 years | 1 year 8 months 12 days
Standard & Poor's, BBB Rating [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 2 | $ 3
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 1,220 | $ 1,164
Derivative Average Remaining Maturity | [1],[3] | 3 years 6 months | 4 years
Standard & Poor's, BB+ Rating [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 0 | $ 0
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 10 | $ 0
Derivative Average Remaining Maturity | [1],[3] | 8 months 12 days | 0 years
Single Name Credit Default Swaps [Member] | Standard Poors AAA To A Ratings [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 11 | $ 2
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 287 | $ 142
Derivative Average Remaining Maturity | [1],[3] | 15 years | 1 year 8 months 12 days
Single Name Credit Default Swaps [Member] | Standard & Poor's, BBB Rating [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 2 | $ 3
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 232 | $ 291
Derivative Average Remaining Maturity | [1],[3] | 1 year 7 months 6 days | 1 year 10 months 24 days
Single Name Credit Default Swaps [Member] | Standard & Poor's, BB+ Rating [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 0 | $ 0
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 10 | $ 0
Derivative Average Remaining Maturity | [1],[3] | 8 months 12 days | 0 years
Credit Default Swaps Referencing Indices [Member] | Standard & Poor's, BBB Rating [Member] |  |  |
Credit Derivatives [Line Items] |  |  |
Credit Risk Derivatives, at Fair Value, Net | [1] | $ 0 | $ 0
Maximum Potential Future Exposure on Credit Risk Derivatives | [1],[2] | $ 988 | $ 873
Derivative Average Remaining Maturity | [1],[3] | 3 years 10 months 24 days | 4 years 8 months 12 days
[1] | The rating agency designations are based on ratings from Standard and Poor’s (“S&P”).
[2] | Assumes the value of the referenced credit obligations is zero.
[3] | The weighted average years to maturity of the credit default swaps is calculated based on weighted average notional amounts

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- Definition Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions. + 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 (b)(1) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5708775-113959 + Details
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Balance Type: | credit
Period Type: | instant

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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. + Details
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- Definition Fair value of credit risk derivative asset after deduction of credit risk derivative liability. + 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 (c) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5708775-113959 + Details
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- Definition Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Details
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