| **Investments (Tables)**                                                                                                            | 6 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 June 30, 2014 cost gains losses valueFixed maturity securities:        States, municipalities and political subdivisions $3,205 $170 $5 $3,370Convertibles and bonds with warrants attached 7 — — 7United States government 7 — — 7Government-sponsored enterprises 221 — 13 208Foreign government 10 — — 10Commercial mortgage-backed  220 7 1 226Corporate  5,049 509 3 5,555Subtotal 8,719 686 22 9,383Equity securities:        Common equities 2,458 1,992 3 4,447Nonredeemable preferred equities 124 35 1 158Subtotal 2,582 2,027 4 4,605Total $11,301 $2,713 $26 $13,988At December 31, 2013        Fixed maturity securities:        States, municipalities and political subdivisions $3,107 $125 $21 $3,211Convertibles and bonds with warrants attached 17 — — 17United States government 7 — — 7Government-sponsored enterprises 227 — 27 200Foreign government 10 — — 10Commercial mortgage-backed  148 — 5 143Corporate  5,122 433 22 5,533Subtotal 8,638 558 75 9,121Equity securities:        Common equities 2,396 1,818 1 4,213Nonredeemable preferred equities 127 38 3 162Subtotal 2,523 1,856 4 4,375Total $11,161 $2,414 $79 $13,496                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| 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 gross unrealized losses by investment category and by the duration of the securities’ continuous unrealized loss positions:(In millions) Less than 12 months 12 months or more Total Total  Fair Unrealized Fair Unrealized fair unrealizedAt June 30, 2014 value losses value losses value lossesFixed maturity securities:            States, municipalities and political    subdivisions $61 $1 $267 $4 $328 $5United States government — — 1 — 1 —Government-sponsored enterprises 10 — 175 13 185 13Foreign government — — 10 — 10 —Commercial mortgage-backed  — — 32 1 32 1Corporate  49 — 127 3 176 3Subtotal 120 1 612 21 732 22Equity securities:            Common equities 39 — 79 3 118 3Nonredeemable preferred equities 5 — 17 1 22 1Subtotal 44 — 96 4 140 4Total $164 $1 $708 $25 $872 $26At December 31, 2013            Fixed maturity securities:            States, municipalities and political    subdivisions $490 $18 $42 $3 $532 $21United States government 1 — — — 1 —Government-sponsored enterprises 199 27 1 — 200 27Foreign government 10 — — — 10 —Commercial mortgage-backed  125 5 — — 125 5Corporate  572 20 43 2 615 22Subtotal 1,397 70 86 5 1,483 75Equity securities:            Common equities 77 1 — — 77 1Nonredeemable preferred equities 42 3 — — 42 3Subtotal 119 4 — — 119 4Total $1,516 $74 $86 $5 $1,602 $79              |
| 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 June 30, Six months ended June 30,  2014 2013 2014 2013Investment income summary:        Interest on fixed maturities $103 $103 $207 $205Dividends on equity securities 34 30 66 57Other investment income  1 — 2 1Total 138 133 275 263Less investment expenses 2 2 4 4Total $136 $131 $271 $259         Realized investment gains and losses summary:        Fixed maturities:        Gross realized gains $4 $2 $6 $4Gross realized losses — — — —Other-than-temporary impairments — — — (2)Equity securities:        Gross realized gains 16 12 34 49Gross realized losses — — — —Other-than-temporary impairments — — (1) —Securities with embedded derivatives (3) — (4) 1Other (3) — 1 3Total $14 $14 $36 $55         Change in unrealized gains and losses summary:        Fixed maturities $93 $(282) $181 $(307)Equity securities 142 38 171 419Net change in pension actuarial loss and prior  service cost — 3 (1) 5Adjustment to deferred acquisition costs and life  policy reserves (5) 26 (8) 29Other 6 (2) 8 (5)Income taxes on above (82) 76 (123) (49)Total $154 $(141) $228 $92                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |

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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).
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