| **Fair Value Measurements (Tables)**                                                         | 9 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 September 30, 2015, and December 31, 2014. We do not have any material liabilities carried at fair value. There were no transfers between Level 1 and Level 2.(Dollars in millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt September 30, 2015    Fixed maturities, available for sale:        Corporate  $— $5,568 $41 $5,609States, municipalities and political subdivisions — 3,557 — 3,557Commercial mortgage-backed — 292 — 292Government-sponsored enterprises — 276 — 276Foreign government — 10 — 10Convertibles and bonds with warrants attached — 8 — 8United States government 4 — — 4Subtotal 4 9,711 41 9,756Common equities, available for sale 4,313 — — 4,313Nonredeemable preferred equities, available for sale — 211 2 213Short-term investments — 75 — 75Separate accounts taxable fixed maturities  — 754 — 754Top Hat savings plan mutual funds and common  equity (included in Other assets) 20 — — 20Total $4,337 $10,751 $43 $15,131At December 31, 2014        Fixed maturities, available for sale:        Corporate  $— $5,508 $18 $5,526States, municipalities and political subdivisions — 3,443 — 3,443Commercial mortgage-backed  — 259 — 259Government-sponsored enterprises — 208 — 208Foreign government — 10 — 10Convertibles and bonds with warrants attached — 7 — 7United States government 7 — — 7Subtotal 7 9,435 18 9,460Common equities, available for sale 4,679 — — 4,679Nonredeemable preferred equities, available for sale — 177 2 179Separate accounts taxable fixed maturities  — 731 — 731Top Hat savings plan mutual funds and common  equity (included in Other assets) 18 — — 18Total $4,704 $10,343 $20 $15,067                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)                |  (Dollars in millions) Asset fair value measurements using significant unobservable inputs (Level 3)  Corporatefixedmaturities Commercialmortgage-backed fixed maturities States,municipalitiesand politicalsubdivisionsfixed maturities Nonredeemable preferredequities TotalBeginning balance, June 30, 2015 $18 $— $1 $2 $21Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income 1 — — — 1Purchases 22 — — — 22Sales — — — — —Transfers into Level 3 — — — — —Transfers out of Level 3 — — (1) — (1)Ending balance, September 30, 2015 $41 $— $— $2 $43           Beginning balance, June 30, 2014 $9 $— $— $2 $11Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income — — — — —Purchases — — — — —Sales — — — — —Transfers into Level 3 19 — — — 19Transfers out of Level 3 — — — — —Ending balance, September 30, 2014 $28 $— $— $2 $30           The following table provides the change in Level 3 assets for the nine months ended September 30:(Dollars in millions)Asset fair value measurements using significant unobservable inputs (Level 3)  Corporatefixedmaturities Commercialmortgage-backed fixed maturities States,municipalitiesand politicalsubdivisionsfixed maturities Nonredeemable preferredequities TotalBeginning balance, January 1, 2015 $18 $— $— $2 $20Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income 1 — — — 1Purchases 22 — — — 22Sales — — — — —Transfers into Level 3 — — 1 — 1Transfers out of Level 3 — — (1) — (1)Ending balance, September 30, 2015 $41 $— $— $2 $43           Beginning balance, January 1, 2014 $2 $— $— $2 $4Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income — — — — —Purchases — — — — —Sales — — — — —Transfers into Level 3 26 5 — — 31Transfers out of Level 3 — (5) — — (5)Ending balance, September 30, 2014 $28 $— $— $2 $30            |
| 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:(Dollars in millions)   Book value Principal amount      September 30, December 31, September 30, December 31,Interest rate Year of issue   2015 2014 2015 20146.900% 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 372 372 374 374    Total $791 $791 $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:(Dollars in millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt September 30, 2015    Life policy loans $— $— $40 $40         At December 31, 2014        Life policy loans $— $— $39 $39                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| 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:(Dollars in millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt September 30, 2015    Note payable $— $35 $— $356.900% senior debentures, due 2028 — 34 — 346.920% senior debentures, due 2028 — 498 — 4986.125% senior notes, due 2034 — 441 — 441Total $— $1,008 $— $1,008         At December 31, 2014        Note payable $— $49 $— $496.900% senior debentures, due 2028 — 34 — 346.920% senior debentures, due 2028 — 496 — 4966.125% senior notes, due 2034 — 449 — 449Total $— $1,028 $— $1,028                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| 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:(Dollars in millions) Quoted prices inactive markets foridentical assets(Level 1) Significant otherobservable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt September 30, 2015    Deferred annuities $— $— $892 $892Structured settlements — 208 — 208Total $— $208 $892 $1,100         At December 31, 2014        Deferred annuities $— $— $897 $897Structured settlements — 217 — 217Total $— $217 $897 $1,114                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |

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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
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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No definition available.
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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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