| **Employee Retirement Benefits (Tables)**             | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                |
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| **Compensation and Retirement Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                          |
| Schedule of Defined Benefit Plans Disclosures         | The 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     |

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| - References
No definition available.
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| - Definition
Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans.
+ References
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