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Investments - Valuation changes included in net income for investments (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items] |  |
Total | $ 1,222 | $ (12)
Equity securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total | 1,073 | (261)
Limited partnership interests |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Total | $ 149 | $ 249

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