|**Long-Term Debt And Capital Lease Obligation (Tables)**    | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                             
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|**Long-term Debt and Capital Lease Obligations [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Book Value And Principal Amounts Of Long-Term Debt          | This table summarizes the principal amounts of our long-term debt excluding unamortized discounts, none of which are encumbered by rating triggers:(Dollars in millions)Book valuePrincipal amountInterest rateYear ofissueAt December 31,At December 31,20182017201820176.900%1998Senior debentures, due 2028$27$26$28$286.920%2005Senior debentures, due 20283913913913916.125%2004Senior notes, due 2034370370374374Total$788$787$793$793
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|(Dollars in millions)                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Interest rate                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|6.900%                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                             
|6.920%                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                             
|6.125%                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|Capital Lease Payments Over Next Five Years                 | Below are the expected capital lease obligations, which includes$3 millionof interest, that we expect to pay over the next six years:(Dollars in millions)Years ended December 31,201920202021202220232024Capital lease obligations$16$12$9$6$4$2                                                                                                                                                                                           
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|(Dollars in millions)                                       | Years ended December 31,                                                                                                                                                                                                                                                                                                                                                                                                                    
|                                                            | 2019                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Capital lease obligations                                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                           
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