| **Employee Retirement Benefits**                      | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Compensation and Retirement Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Employee Retirement Benefits                          | Employee Retirement BenefitsThe following summarizes the components of net periodic benefit cost for our qualified and supplemental pension plans:(Dollars in millions)Three months ended March 31, 2016 2015Service cost$3 $3Interest cost3 3Expected return on plan assets(5) (4)Amortization of actuarial loss and prior service cost1 1Net periodic benefit cost$2 $3    See our 2015 Annual Report on Form 10-K, Item 8, Note 13, Employee Retirement Benefits, Page 146, for information on our retirement benefits. We made matching contributions totaling $4 million to our 401(k) and Top Hat savings plans during both the first quarters of 2016 and 2015.  We contributed $5 million to our qualified pension plan during the first quarter of 2016. We do not anticipate further contributions to our qualified pension plan during the remainder of 2016. |

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| - Definition
The entire disclosure for pension and other postretirement benefits.
+ References
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