| **Fair Value Measurements**           | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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| **Fair Value Disclosures [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| Fair Value Measurements               | Fair Value Measurements In accordance with accounting guidance for fair value measurements and disclosures, we categorized our financial instruments, based on the priority of the observable and market-based data for the valuation technique used, into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices with readily available independent data in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable market inputs (Level 3). When various inputs for measurement fall within different levels of the fair value hierarchy, the lowest observable input that has a significant impact on fair value measurement is used. Our valuation techniques have not changed from those used at December 31, 2015, and ultimately management determines fair value. See our 2015 Annual Report on Form 10-K, Item 8, Note 3, Fair Value Measurements, Page 133, for information on characteristics and valuation techniques used in determining fair value.Fair Value Disclosures for AssetsThe following tables illustrate the fair value hierarchy for those assets measured at fair value on a recurring basis at September 30, 2016, and December 31, 2015. 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, 2016    Fixed maturities, available for sale:        Corporate  $— $5,940 $42 $5,982States, municipalities and political subdivisions — 3,840 — 3,840Commercial mortgage-backed — 308 — 308Government-sponsored enterprises — 108 — 108Foreign government — 10 — 10Convertibles and bonds with warrants attached — 5 — 5United States government 4 — — 4Subtotal 4 10,211 42 10,257Common equities, available for sale 5,077 — — 5,077Nonredeemable preferred equities, available for sale — 227 — 227Separate accounts taxable fixed maturities  — 753 — 753Top Hat savings plan mutual funds and common  equity (included in Other assets) 24 — — 24Total $5,105 $11,191 $42 $16,338At December 31, 2015        Fixed maturities, available for sale:        Corporate  $— $5,402 $51 $5,453States, municipalities and political subdivisions — 3,611 — 3,611Commercial mortgage-backed  — 289 — 289Government-sponsored enterprises — 278 — 278Foreign government — 10 — 10Convertibles and bonds with warrants attached — 5 — 5United States government 4 — — 4Subtotal 4 9,595 51 9,650Common equities, available for sale 4,485 — — 4,485Nonredeemable preferred equities, available for sale — 218 3 221Separate accounts taxable fixed maturities  — 736 1 737Top Hat savings plan mutual funds and common  equity (included in Other assets) 21 — — 21Total $4,510 $10,549 $55 $15,114          Each financial instrument that was deemed to have significant unobservable inputs when determining valuation is identified in the following tables by security type with a summary of changes in fair value as of September 30, 2016. Total Level 3 assets continue to be less than 1 percent of financial assets measured at fair value in the condensed consolidated balance sheets. Assets presented in the table below were valued based primarily on broker/dealer quotes for which there is a lack of transparency as to inputs used to develop the valuations. Transfers into Level 3 included situations where a fair value quote was not provided by the company's nationally recognized pricing vendor and as a result the price was stale or had been replaced with a broker quote where the inputs had not been corroborated to be market observable resulting in the security being classified as Level 3. Transfers out of Level 3 included situations where a broker quote was used in the prior period and a fair value quote became available from the company's nationally recognized pricing vendor in the current period. The quantitative detail of these unobservable inputs is neither provided nor reasonably available to us. The following table provides the change in Level 3 assets for the three months ended September 30: (Dollars in millions) Asset fair value measurements using significant unobservable inputs (Level 3)  Corporatefixedmaturities Separate accounts taxable fixed maturities States,municipalitiesand politicalsubdivisionsfixed maturities Nonredeemable preferredequities TotalBeginning balance, July 1, 2016 $52 $1 $— $— $53Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income 1 — — — 1Purchases — — — — —Sales (1) — — — (1)Transfers into Level 3 — — — — —Transfers out of Level 3 (10) (1) — — (11)Ending balance, September 30, 2016 $42 $— $— $— $42           Beginning balance, July 1, 2015 $18 $— $1 $2 $21Total gains or losses (realized/unrealized):          Included in net income 1 — — — 1Included in other comprehensive income 22 — — — 22Purchases — — — — —Sales — — — — —Transfers into Level 3 — — — — —Transfers out of Level 3 — — (1) — (1)Ending balance, September 30, 2015 $41 $— $— $2 $43           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 Separateaccountstaxablefixedmaturities  States,municipalitiesand politicalsubdivisionsfixed maturities Nonredeemablepreferredequities TotalBeginning balance, January 1, 2016 $51 $1 $— $3 $55Total gains or losses (realized/unrealized):          Included in net income — — — — —Included in other comprehensive income 1 — — (1) —Purchases 22 — — — 22Sales (1) — — (2) (3)Transfers into Level 3 — — — — —Transfers out of Level 3 (31) (1) — — (32)Ending balance, September 30, 2016 $42 $— $— $— $42           Beginning 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           Additional disclosures for the Level 3 category are not material.Fair Value Disclosures for Assets and Liabilities Not Carried at Fair Value The disclosures below are presented to provide timely information about the effects of current market conditions on financial instruments that are not reported at fair value in our condensed consolidated financial statements. 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   2016 2015 2016 20156.900% 1998 Senior debentures, due 2028 $26 $26 $28 $286.920% 2005 Senior debentures, due 2028 391 391 391 3916.125% 2004 Senior notes, due 2034 369 369 374 374    Total $786 $786 $793 $793              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 other observable inputs (Level 2) Significantunobservableinputs(Level 3) TotalAt September 30, 2016    Note payable $— $20 $— $206.900% senior debentures, due 2028 — 35 — 356.920% senior debentures, due 2028 — 511 — 5116.125% senior notes, due 2034 — 452 — 452Total $— $1,018 $— $1,018         At December 31, 2015        Note payable $— $35 $— $356.900% senior debentures, due 2028 — 31 — 316.920% senior debentures, due 2028 — 480 — 4806.125% senior notes, due 2034 — 425 — 425Total $— $971 $— $971          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, 2016    Life policy loans $— $— $41 $41         At December 31, 2015        Life policy loans $— $— $40 $40          Outstanding principal and interest for these life policy loans totaled $30 million and $31 million at September 30, 2016, and December 31, 2015, respectively. 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, 2016    Deferred annuities $— $— $881 $881Structured settlements — 218 — 218Total $— $218 $881 $1,099         At December 31, 2015        Deferred annuities $— $— $886 $886Structured settlements — 208 — 208Total $— $208 $886 $1,094         Recorded reserves for the deferred annuities were $864 million and $860 million at September 30, 2016, and December 31, 2015, respectively.  Recorded reserves for the structured settlements were $170 million and $174 million at September 30, 2016, and December 31, 2015, respectively. |

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The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.
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