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Fair Value Measurements (Details 4) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 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 | $ 175 | $ 313 | $ 366 | $ 820
Realized Gains | 9 | 29 | 28 | 50
Realized Losses | (11) | (29) | (27) | (44)
Interest and Dividend Income | $ 10 | $ 10 | $ 20 | $ 19

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