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Investments (Narrative) (Detail) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) Security | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) Security | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Investment [Line Items] |  |  |  |  |
Net unrealized appreciation (depreciation) included in OCI | $ (2) | $ 1 | $ (6) | $ (2) |
Unrealized appreciation(depreciation) portion of AOCI with OTTI included in AOCI | $ 1 |  | $ 1 |  | $ 7
Percentage of mortgage-backed securities represented by investments in US government agency bonds | 82.00% |  | 82.00% |  | 83.00%
Moodys Historical Mean Recovery Rate |  |  | 42.00% |  |
Company Assumed Recovery Rate |  |  | 32.00% |  |
Operating Lease, Impairment Loss |  |  | $ 22 |  |
Available-for-sale Equity Securities, Amortized Cost Basis | $ 843 |  | 843 |  | $ 737
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, at fair value | $ 843 |  | $ 843 |  | 937
Total number of fixed maturities | Security | 31,196 |  | 31,196 |  |
Number of fixed maturities in an unrealized loss position | Security | 17,978 |  | 17,978 |  |
Largest single unrealized loss in the fixed maturities | $ 13 |  | $ 13 |  |
Restricted assets in fixed maturities and short-term investments | 21,000 |  | 21,000 |  | 23,300
Restricted assets in cash | 104 |  | 104 |  | $ 123
Corporate securities |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Credit losses recognized in net income | 8 | 3 | 9 | 5 |
Mortgage-backed securities |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Credit losses recognized in net income | $ 0 | $ 0 | 0 | $ 0 |
Junior Subordinated Debt [Member] | Chubb INA Senior Notes Due 2037 [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Gain (Loss) on Extinguishment of Debt |  |  | $ (36) |  |

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