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Fair Value of Assets and Liabilities - Quantitative information about the significant unobservable inputs used in level 3 fair value measurements (Details) - Derivatives embedded in life and annuity contracts - Equity-indexed and forward starting options - Stochastic cash flow model - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Quantitative information about the significant unobservable inputs |  |
Liabilities, fair value | $ (232) | $ (252)
Weighted average projected option cost (as a percent) | 1.74% | 1.74%
Minimum |  |
Quantitative information about the significant unobservable inputs |  |
Projected option cost (as a percent) | 1.00% | 1.00%
Maximum |  |
Quantitative information about the significant unobservable inputs |  |
Projected option cost (as a percent) | 2.20% | 2.20%

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- Definition Represents the percentage of projected option cost as an input to measure fair value. + References No definition available. + Details
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- Definition Represents the weighted average percentage of projected option cost as an input to measure fair value. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity. + References No definition available. + Details
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