Derivative Financial Instruments and Off-balance sheet Financial Instruments - CDS notional amounts by credit rating (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Term of credit default swaps	5 years
Credit Derivatives
Derivative, notional amount	$ 5,191	$ 3,478
Credit default contracts
Credit Derivatives
Derivative, notional amount	759	9
Fair value	13	0
Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	9	9
Fair value	0	0
Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	750
Fair value	13
AAA \| Credit default contracts
Credit Derivatives
Derivative, notional amount	6	0
AAA \| Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	0	0
AAA \| Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	6
AA \| Credit default contracts
Credit Derivatives
Derivative, notional amount	12	0
AA \| Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	0	0
AA \| Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	12
A \| Credit default contracts
Credit Derivatives
Derivative, notional amount	156	0
A \| Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	0	0
A \| Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	156
BBB \| Credit default contracts
Credit Derivatives
Derivative, notional amount	492	0
BBB \| Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	0	0
BBB \| Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	492
BB and lower \| Credit default contracts
Credit Derivatives
Derivative, notional amount	93	9
BB and lower \| Credit default contracts \| Single name \| Corporate
Credit Derivatives
Derivative, notional amount	9	$ 9
BB and lower \| Credit default contracts \| Index \| Corporate
Credit Derivatives
Derivative, notional amount	$ 84

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- Definition

Term of the credit risk derivative contract, 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
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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 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
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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
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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