| **Employee Retirement Benefits (Tables)**             | 6 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 June 30, Six months ended June 30,  2017 2016 2017 2016Service cost $2 $2 $5 $5Interest cost 4 4 7 7Expected return on plan assets (5) (4) (10) (9)Amortization of actuarial loss and prior service cost — 1 1 2Net periodic benefit cost $1 $3 $3 $5          |

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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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