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Investments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract] |  |
Shadow Adjustments | $ 1,300 | $ 964
Additional other than temporary impairment losses | $ 0 |

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