| **Income Taxes**                     | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Income Tax Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Income Taxes                         | Income TaxesAs of September 30, 2016, and December 31, 2015, we had no liability for unrecognized tax benefits.  The differences between the 35 percent statutory federal income tax rate and our effective income tax rate were as follows:(Dollars in millions) Three months ended September 30, Nine months ended September 30,  2016 2015 2016 2015Tax at statutory rate: $88 35.0 % $85 35.0 % $239 35.0 % $233 35.0 %Increase (decrease) resulting from:                Tax-exempt income from municipal bonds (8) (3.2) (9) (3.7) (25) (3.7) (25) (3.8)Dividend received exclusion (8) (3.2) (8) (3.3) (24) (3.5) (23) (3.5)Other 1 0.3 1 0.4 3 0.4 2 0.4Provision for income taxes $73 28.9 % $69 28.4 % $193 28.2 % $187 28.1 %                  The provision for federal income taxes is based upon filing a consolidated income tax return for the company and its subsidiaries. As of September 30, 2016, we had no operating or capital loss carry forwards. |

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The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
+ References
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