| **Investments (Tables)**                                                                                                            | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
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| **Investments [Abstract]**                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Analysis Of Cost Or Amortized Cost, Gross Unrealized Gains And Losses And Fair Value for Investments                                | The following table provides cost or amortized cost, gross unrealized gains, gross unrealized losses and fair value for our invested assets:(In millions) Cost or        amortized Gross unrealized FairAt September 30, 2013 cost gains losses valueFixed maturities:        States, municipalities and political subdivisions $3,046 $146 $17 $3,175Convertibles and bonds with warrants attached 16 — — 16United States government 7 — — 7Government-sponsored enterprises 209 — 19 190Foreign government 10 — — 10Commercial mortgage-backed securities 79 — 3 76Corporate securities 5,135 454 25 5,564Subtotal 8,502 600 64 9,038Equity securities:        Common equities 2,394 1,482 3 3,873Preferred equities 77 34 — 111Subtotal 2,471 1,516 3 3,984Total $10,973 $2,116 $67 $13,022At December 31, 2012        Fixed maturities:        States, municipalities and political subdivisions $3,040 $250 $1 $3,289Convertibles and bonds with warrants attached 31 — — 31United States government 7 1 — 8Government-sponsored enterprises 164 — — 164Foreign government 3 — — 3Commercial mortgage-backed securities 27 1 — 28Corporate securities 4,950 622 2 5,570Subtotal 8,222 874 3 9,093Equity securities:        Common equities 2,270 977 9 3,238Preferred equities 99 37 1 135Subtotal 2,369 1,014 10 3,373Total $10,591 $1,888 $13 $12,466                                                                                                                                                                                                                                                |
| Fair Values And Unrealized Losses by Investment Category And By The Duration Of The Securities' Continuous Unrealized Loss Position | The table below provides fair values and unrealized losses by investment category and by the duration of the securities’ continuous unrealized loss position:(In millions) Less than 12 months 12 months or more Total Total  Fair Unrealized Fair Unrealized fair unrealizedAt September 30, 2013 value losses value losses value lossesFixed maturities:            States, municipalities and political    subdivisions $371 $17 $8 $— $379 $17United States government 1 — — — 1 —Government-sponsored enterprises 190 19 — — 190 19Foreign government 9 — — — 9 —Commercial mortgage-backed securities 62 3 — — 62 3Corporate securities 526 22 35 3 561 25Subtotal 1,159 61 43 3 1,202 64Equity securities:            Common equities 74 3 — — 74 3Preferred equities 4 — — — 4 —Subtotal 78 3 — — 78 3Total $1,237 $64 $43 $3 $1,280 $67At December 31, 2012            Fixed maturities:            States, municipalities and political    subdivisions $53 $1 $— $— $53 $1Government-sponsored enterprises 1 — — — 1 —Corporate securities 58 1 17 1 75 2Subtotal 112 2 17 1 129 3Equity securities:            Common equities 107 9 — — 107 9Preferred equities 4 1 — — 4 1Subtotal 111 10 — — 111 10Total $223 $12 $17 $1 $240 $13 |
| Investment Income, Realized Investment Gains And Losses And Change In Unrealized Investment Gains And Losses                        | The following table provides investment income, realized investment gains and losses, the change in unrealized investment gains and losses, and other items:(In millions) Three months ended September 30, Nine months ended September 30,  2013 2012 2013 2012Investment income summary:        Interest on fixed maturities $104 $105 $309 $317Dividends on equity securities 30 28 87 81Other investment income  1 1 2 3Total 135 134 398 401Less investment expenses 2 2 6 6Total $133 $132 $392 $395         Realized investment gains and losses summary:        Fixed maturities:        Gross realized gains $5 $14 $9 $30Gross realized losses — — — —Other-than-temporary impairments — — (2) —Equity securities:        Gross realized gains 15 1 64 30Gross realized losses — — — (1)Other-than-temporary impairments — (2) — (32)Securities with embedded derivatives — (4) 1 1Other 2 1 5 1Total $22 $10 $77 $29         Change in unrealized gains and losses summary:        Fixed maturities $(28) $110 $(335) $188Equity securities 90 143 509 240Amortization of pension actuarial loss and  prior service cost 2 2 7 5Adjustment to deferred acquisition costs and  life policy reserves 9 (6) 38 (21)Other (2) — (7) 5Income taxes on above (25) (88) (74) (147)Total $46 $161 $138 $270                                                                                                                                                                                                                                                                                                       |

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| - Definition
Tabular disclosure of investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities, and income or expense derived from the amortization of investment related discounts or premiums; proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales; components of comprehensive income.
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No definition available.
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| - Definition
Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.
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| - Definition
For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).
+ References
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