| **Investments (Tables)**                                                                                                            | 3 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 March 31, 2013 cost gains losses valueFixed maturities:        States, municipalities and political subdivisions $3,006 $233 $1 $3,238Convertibles and bonds with warrants attached 27 — — 27United States government 7 1 — 8Government-sponsored enterprises 168 — 1 167Foreign government 13 — — 13Commercial mortgage-backed securities 38 1 — 39Corporate securities 5,064 615 2 5,677Subtotal 8,323 850 4 9,169Equity securities:        Common equities 2,331 1,346 2 3,675Preferred equities 85 41 — 126Subtotal 2,416 1,387 2 3,801Total $10,739 $2,237 $6 $12,970At 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  Fair Unrealized Fair Unrealized Fair UnrealizedAt March 31, 2013 value losses value losses value lossesFixed maturities:            States, municipalities and political subdivisions $103 $1 $— $— $103 $1Government-sponsored enterprises 107 1 — — 107 1Commercial mortgage-backed securities 16 — — — 16 —Corporate securities 118 1 13 1 131 2Subtotal 344 3 13 1 357 4Equity securities:            Common equities 74 2 — — 74 2Preferred equities 1 — — — 1 —Subtotal 75 2 — — 75 2Total $419 $5 $13 $1 $432 $6At 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 realized investment gains and losses and the change in unrealized investment gains and losses and other items:(In millions) Three months ended March 31,  2013 2012Investment income summary:    Interest on fixed maturities $102 $106Dividends on equity securities 27 26Other investment income  1 1Total 130 133Less investment expenses 2 2Total $128 $131     Realized investment gains and losses summary:    Fixed maturities:    Gross realized gains $2 $3Gross realized losses — —Other-than-temporary impairments (2) —Equity securities:    Gross realized gains 37 23Gross realized losses — —Other-than-temporary impairments — (16)Securities with embedded derivatives 1 4Other 3 (1)Total $41 $13     Change in unrealized gains and losses summary:    Fixed maturities $(25) $49Equity securities 381 179Adjustment to deferred acquisition costs and life policy reserves 3 (7)Amortization of pension actuarial loss and prior service cost 2 2Other (3) 2Income taxes on above (125) (79)Total $233 $146                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27198-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph a, b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph a, b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27337-111563Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 19, 20, 21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803Reference 10: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563
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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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