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Investments - Valuation changes included in net income for investments (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2018
Investment [Line Items] |  |
Total valuation changes | $ 122 | $ 177
Equity securities |  |
Investment [Line Items] |  |
Total valuation changes | 94 | 71
Limited partnership interests |  |
Investment [Line Items] |  |
Total valuation changes | $ 28 | $ 106

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- Definition Realized Gain (Loss), Fair Value Recognized In Net Income + References No definition available. + Details
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- Definition Line items represent reporting 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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 12 -Sentence Column A + Details
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- Details
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- Details
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