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Investments - Equity securities reported at fair value (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Debt Securities, Trading, and Equity Securities, FV-NI [Line Items] |  |
Equity securities, at fair value | $ 1,786 | $ 1,662
Common stocks |  |
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items] |  |
Equity securities, at cost | 1,099 |
Equity securities, at fair value | 1,154 |
Equity securities, fair value in excess of cost | 55 |
Perpetual preferred stocks |  |
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items] |  |
Equity securities, at cost | 632 |
Equity securities, at fair value | 632 |
Equity securities, fair value in excess of cost | 0 |
Equity securities |  |
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items] |  |
Equity securities, at cost | 1,731 |
Equity securities, at fair value | 1,786 |
Equity securities, fair value in excess of cost | $ 55 |

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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References No definition available. + Details
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- Definition Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. + References No definition available. + Details
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI) in excess of the cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. + References No definition available. + Details
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