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Investments Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Original Non-Credit Loss at Time Credit Impairment (Detail) - Fixed maturities - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items] |  |
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities | $ (20.0) | $ (43.9)
Residential mortgage-backed securities |  |
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items] |  |
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities | (19.7) | (43.3)
Commercial mortgage-backed securities |  |
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items] |  |
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities | $ (0.3) | $ (0.6)

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- Definition Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is pre-tax. + References No definition available. + Details
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- Definition Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items] + References No definition available. + Details
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