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Fair Value of Assets and Liabilities - Narrative (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2020 | Dec. 31, 2019
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Fair value | $ 66,551 | $ 59,044
Significant unobservable inputs (Level 3) |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Assets at fair value | 855 | 738
Recurring | Significant unobservable inputs (Level 3) |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Fair value | 437 | 342
Assets at fair value | 855 | 738
Fixed Income Securities Valued Based on Nonbinding Broker Quotes |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Assets at fair value | 126 | 50
Municipal Not Rated by Third Party Credit Rating Agencies |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Assets at fair value | 34 | $ 36
Limited partnership interests |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Commitments to invest in limited partnership interests | $ 388 |
Limited partnership interests | Minimum |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Investment assets, useful life | 10 years |
Limited partnership interests | Maximum |  |
Fair value of assets and liabilities measured on recurring and non-recurring basis |  |
Investment assets, useful life | 12 years |

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- Definition This element represents commitments to acquire financial interests or instruments, to allow for additional participation in certain limited partnership investments. Because the equity investments in the limited partnerships are not actively traded, it is not practical to estimate the fair value of these commitments. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + 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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