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Investments (Narrative) (Detail) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2017 USD ($) Security | Mar. 31, 2016 USD ($) | Dec. 31, 2016 USD ($)
Investment [Line Items] |  |  |
Net unrealized appreciation (depreciation) included in OCI | $ 0 | $ 23 |
Unrealized appreciation (depreciation) portion of AOCI with OTTI included in AOCI | $ 10 |  | $ 10
Percentage of mortgage-backed securities represented by investments in US government agency bonds | 82.00% |  | 81.00%
Total number of fixed maturities | Security | 31,098 |  |
Number of equity securities in an unrealized loss position | Security | 70 |  |
Total number of equity securities | Security | 325 |  |
Largest single unrealized loss in the equity securities | $ 1 |  |
Restricted assets in fixed maturities and short-term investments | 20,600 |  | $ 20,100
Restricted assets in cash | $ 97 |  | $ 103
Moodys Historical Mean Recovery Rate | 42.00% |  |
Company Assumed Recovery Rate | 32.00% |  |
Number of fixed maturities in an unrealized loss position | Security | 9,408 |  |
Largest single unrealized loss in the fixed maturities | $ 6 |  |
Corporate [Member] |  |  |
Investment [Line Items] |  |  |
Credit losses recognized in net income | 1 | 17 |
Collateralized Mortgage Backed Securities [Member] |  |  |
Investment [Line Items] |  |  |
Credit losses recognized in net income | $ 0 | $ 0 |

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