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Derivative Financial Instruments - CDS notional amounts by credit rating and fair value of protection sold (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |
Term of credit default swaps (in years) | 5 years |
Credit Derivatives |  |
Notional amount | $ 4,690 | $ 3,388
Credit default contracts |  |
Credit Derivatives |  |
Notional amount | 265 | 105
Fair value | 4 | 1
Credit default contracts | Single name | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 15 | 25
Fair value | 0 | 0
Credit default contracts | Index | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 250 | 80
Fair value | 4 | 1
AA | Credit default contracts |  |
Credit Derivatives |  |
Notional amount | 4 | 1
AA | Credit default contracts | Single name | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 0 | 0
AA | Credit default contracts | Index | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 4 | 1
A | Credit default contracts |  |
Credit Derivatives |  |
Notional amount | 44 | 29
A | Credit default contracts | Single name | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 0 | 10
A | Credit default contracts | Index | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 44 | 19
BBB | Credit default contracts |  |
Credit Derivatives |  |
Notional amount | 186 | 55
BBB | Credit default contracts | Single name | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 10 | 10
BBB | Credit default contracts | Index | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 176 | 45
BB and lower | Credit default contracts |  |
Credit Derivatives |  |
Notional amount | 31 | 20
BB and lower | Credit default contracts | Single name | Corporate debt |  |
Credit Derivatives |  |
Notional amount | 5 | 5
BB and lower | Credit default contracts | Index | Corporate debt |  |
Credit Derivatives |  |
Notional amount | $ 26 | $ 15

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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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 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959 + Details
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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=109980867&loc=SL5708775-113959 + Details
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- References No definition available. + Details
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