| **Fair Value Measurements (Tables)**                                                         | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Fair Value Hierarchy for Assets Measured at Fair Value on a Recurring Basis                  | The following tables illustrate the fair value hierarchy for those assets measured at fair value on a recurring basis at March 31, 2014, and December 31, 2013. We do not have any material liabilities carried at fair value. There were no transfers between Level 1 and Level 2.(In millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt March 31, 2014    Fixed maturities, available for sale:        States, municipalities and political subdivisions $— $3,244 $— $3,244Convertibles and bonds with warrants attached — 17 — 17United States government 7 — — 7Government-sponsored enterprises — 191 — 191Foreign government — 10 — 10Commercial mortgage-backed — 201 5 206Corporate  — 5,497 8 5,505Subtotal 7 9,160 13 9,180Common equities, available for sale 4,257 — — 4,257Nonredeemable preferred equities, available for sale — 167 2 169Separate accounts taxable fixed maturities  — 700 — 700Top Hat Savings Plan mutual funds and common equity (included in Other assets) 17 — — 17Total $4,281 $10,027 $15 $14,323At December 31, 2013        Fixed maturities, available for sale:        States, municipalities and political subdivisions $— $3,211 $— $3,211Convertibles and bonds with warrants attached — 17 — 17United States government 7 — — 7Government-sponsored enterprises — 200 — 200Foreign government — 10 — 10Commercial mortgage-backed  — 143 — 143Corporate  — 5,531 2 5,533Subtotal 7 9,112 2 9,121Common equities, available for sale 4,213 — — 4,213Nonredeemable preferred equities, available for sale — 160 2 162Separate accounts taxable fixed-maturities  — 682 — 682Top Hat Savings Plan mutual funds and common equity (included in Other assets) 14 — — 14Total $4,234 $9,954 $4 $14,192           |
| Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] | This table summarizes the book value and principal amounts of our long-term debt: (In millions)     Book value Principal amount      March 31, December 31, March 31, December 31,Interest rate Year of issue   2014 2013 2014 20136.900% 1998 Senior debentures, due 2028 $28 $28 $28 $286.920% 2005 Senior debentures, due 2028 391 391 391 3916.125% 2004 Senior notes, due 2034 371 371 374 374    Total $790 $790 $793 $793                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Fair Value of Life Policy Loans                                                              | The following table shows the fair value of our life policy loans, included in other invested assets, subject to fair value disclosure requirements: (In millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt March 31, 2014    Life policy loans $— $— $44 $44         At December 31, 2013        Life policy loans $— $— $45 $45                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Debt                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Fair Values of Deferred Annuities, Structured Settlements and Other Items                    | The following table shows fair values of our note payable and long-term debt subject to fair value disclosure requirements: (In millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt March 31, 2014    Note payable $— $104 $— $1046.900% senior debentures, due 2028 — 32 — 326.920% senior debentures, due 2028 — 470 — 4706.125% senior notes, due 2034 — 419 — 419Total $— $1,025 $— $1,025         At December 31, 2013        Note payable $— $104 $— $1046.900% senior debentures, due 2028 — 30 — 306.920% senior debentures, due 2028 — 458 — 4586.125% senior notes, due 2034 — 399 — 399Total $— $991 $— $991                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Deferred Annuities, Structured Settlements, And Other                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Fair Values of Deferred Annuities, Structured Settlements and Other Items                    | The following table shows fair values of our deferred annuities and structured settlements, included in life policy and investment contract reserves, subject to fair value disclosure requirements: (In millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt March 31, 2014    Deferred annuities $— $— $900 $900Structured settlements — 212 — 212Total $— $212 $900 $1,112         At December 31, 2013        Deferred annuities $— $— $911 $911Structured settlements — 219 — 219Total $— $219 $911 $1,130                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |

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| - Definition
Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring and/or nonrecurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).
+ References
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| - Definition
Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).
+ References
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| - Definition
Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.
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| - Definition
Tabular disclosure of liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring and/or nonrecurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).  Where the quoted price in an active market for the identical liability is not available, the Level 1 input is the quoted price of an identical liability when traded as an asset.
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| - Definition
Tabular disclosure of information pertaining to carrying amount and estimated fair value of short-term and long-term debt instruments or arrangements, including but not limited to, identification of terms, features, and collateral requirements.
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No definition available.
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