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Fair Value Measurements (Details 4) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Proceeds from the sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income |  |  |  |
Sale Proceeds | $ 261 | $ 269 | $ 627 | $ 1,089
Realized Gains | 3 | 20 | 31 | 70
Realized Losses | (7) | (11) | (34) | (55)
Interest and Dividend Income | $ 11 | $ 9 | $ 31 | $ 28

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