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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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- Definition

Additional Other Than Temporary Impairment Losses Investments Available For Sale Securities

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- Definition

Net Unrealized Gains On Investments Included In Accumulated Other Comprehensive Income

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