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Investments Investments (held-to-maturity credit quality indicator) (Details) - USD ($) $ in Millions | Mar. 31, 2020 | Dec. 31, 2019
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Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 12,070 | $ 12,581
Fixed Maturities Percent of Total Amortized cost | 100.00% |
Standard & Poor's, AAA Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 2,642 |
Fixed Maturities Percent of Total Amortized cost | 22.00% |
Standard & Poor's, AA Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 6,608 |
Fixed Maturities Percent of Total Amortized cost | 55.00% |
Standard & Poor's, A Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 2,371 |
Fixed Maturities Percent of Total Amortized cost | 20.00% |
Standard & Poor's, BBB Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 422 |
Fixed Maturities Percent of Total Amortized cost | 3.00% |
Standard & Poor's, BB Rating [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 21 |
Fixed Maturities Percent of Total Amortized cost | 0.00% |
Other [Member] |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt Securities, Held-to-maturity | $ 6 |
Fixed Maturities Percent of Total Amortized cost | 0.00% |

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- Definition Amount of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: 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=118954083&loc=d3e26610-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563 + Details
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