| **Employee Retirement Benefits (Tables)**             | 9 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 September 30, Nine months ended September 30,  2016 2015 2016 2015Service cost $3 $3 $8 $9Interest cost 4 3 11 10Expected return on plan assets (5) (4) (14) (13)Amortization of actuarial loss and prior service cost 0 1 2 4Net periodic benefit cost $2 $3 $7 $10          |

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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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