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Investments (Narrative) (Detail) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 USD ($) Security | Dec. 31, 2018 USD ($) Security partnerships | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Investment [Line Items] |  |  |  |
Available-for-sale Equity Securities, Amortized Cost Basis |  |  | $ 737 |
Net unrealized appreciation (depreciation) included in OCI |  | $ (4) | (2) |
AOCI Portion Attributable to change of FV of investments with OTTI | $ 1 | 1 | 7 |
Portion of gross unrealized loss represented by the United States Treasury and Agency obligations | $ 630 | $ 630 |  |
Moodys historical mean recovery rate |  | 42.00% |  |
Limited partnerships number | partnerships |  | 145 |  |
Number of fixed maturities in an unrealized loss position | Security | 19,606 | 19,606 |  |
Total number of fixed maturities | Security | 31,054 | 31,054 |  |
Largest single unrealized loss in the fixed maturities | $ 10 | $ 10 |  |
Restricted assets in fixed maturities and short-term investments | $ 21,000 | $ 21,000 | $ 23,300 |
Percentage of mortgage-backed securities represented by investments in US government agency bonds | 81.00% | 81.00% | 83.00% |
Restricted assets in cash | $ 93 | $ 93 | $ 123 |
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax |  |  | 212 |
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | 12 |
Equity Securities |  |  | 937 |
Operating Lease, Impairment Loss |  | 24 |  |
Impairment of Fixed Assets |  | 23 |  |
Payment to Acquire Other Investments | $ 28 |  |  |
Corporate securities |  |  |  |
Investment [Line Items] |  |  |  |
Credit losses recognized in net income |  | $ 25 | 5 | $ 30
Company assumed recovery rate |  | 32.00% |  |
Collateralized Mortgage Backed Securities [Member] |  |  |  |
Investment [Line Items] |  |  |  |
Credit losses recognized in net income |  | $ 0 | $ 0 | $ 1
Junior Subordinated Debt [Member] | Chubb INA Capital Securities Due 2067 [Member] |  |  |  |
Investment [Line Items] |  |  |  |
Gain (Loss) on Extinguishment of Debt |  | $ (36) |  |

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