| Compensation and Retirement Disclosure [Abstract] | Period [Axis] |
|---|
2016-01-01 - 2016-12-31 |
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Compensation and Retirement Disclosure [Abstract] | |
Schedule of Changes in Benefit Obligation and Plan Assets | The following table sets forth, on an aggregated basis, changes in the benefit obligation and plan assets, the funded status and how the funded status is recognized on our consolidated balance sheets. Table 15.1: Changes in Benefit Obligation and Plan Assets | | | | | | | | | | | | | | | | | | | | Defined Pension
Benefits | | Other Postretirement
Benefits | (Dollars in millions) | | 2016 | | 2015 | | 2016 | | 2015 | Change in benefit obligation: | | | | | | | | | Accumulated benefit obligation as of January 1, | | $ | 185 |
| | $ | 204 |
| | $ | 45 |
| | $ | 55 |
| Service cost | | 2 |
| | 1 |
| | 0 |
| | 0 |
| Interest cost | | 7 |
| | 8 |
| | 2 |
| | 2 |
| Benefits paid | | (14 | ) | | (15 | ) | | (3 | ) | | (3 | ) | Net actuarial loss (gain) | | 0 |
| | (13 | ) | | (5 | ) | | (9 | ) | Accumulated benefit obligation as of December 31, | | $ | 180 |
| | $ | 185 |
| | $ | 39 |
| | $ | 45 |
| Change in plan assets: | | | | | | | | | Fair value of plan assets as of January 1, | | $ | 222 |
| | $ | 239 |
| | $ | 5 |
| | $ | 7 |
| Actual return on plan assets | | 17 |
| | (3 | ) | | 1 |
| | (1 | ) | Employer contributions | | 1 |
| | 1 |
| | 3 |
| | 2 |
| Benefits paid | | (14 | ) | | (15 | ) | | (3 | ) | | (3 | ) | Fair value of plan assets as of December 31, | | $ | 226 |
| | $ | 222 |
| | $ | 6 |
| | $ | 5 |
| Over (under) funded status as of December 31, | | $ | 46 |
| | $ | 37 |
| | $ | (33 | ) | | $ | (40 | ) |
|
Schedule of Amounts Recognized in Balance Sheet | | | | | | | | | | | | | | | | | | | | | Defined Pension
Benefits | | Other Postretirement
Benefits | (Dollars in millions) | | 2016 | | 2015 | | 2016 | | 2015 | Balance sheet presentation as of December 31, | | | | | | | | | Other assets | | $ | 57 |
| | $ | 48 |
| | $ | 0 |
| | $ | 0 |
| Other liabilities | | (11 | ) | | (11 | ) | | (33 | ) | | (40 | ) | Net amount recognized as of December 31, | | $ | 46 |
| | $ | 37 |
| | $ | (33 | ) | | $ | (40 | ) |
|
Schedule of Net Periodic Benefit Cost | The following table presents the components of net periodic benefit costs and other amounts recognized in other comprehensive income. Table 15.2: Components of Net Periodic Benefit Cost | | | | | | | | | | | | | | | | | | | | | | | | | | | | Year Ended December 31, | | | 2016 | | 2015 | | 2014 | | 2016 | | 2015 | | 2014 | (Dollars in millions) | | Defined Pension
Benefits | | Other Postretirement
Benefits | Components of net periodic benefit cost: | | | | | | | | | | | | | Service cost | | $ | 2 |
| | $ | 1 |
| | $ | 1 |
| | $ | 0 |
| | $ | 0 |
| | $ | 0 |
| Interest cost | | 7 |
| | 8 |
| | 8 |
| | 2 |
| | 2 |
| | 2 |
| Expected return on plan assets | | (14 | ) | | (15 | ) | | (14 | ) | | 0 |
| | 0 |
| | 0 |
| Amortization of transition obligation, prior service credit and net actuarial loss (gain) | | 1 |
| | 1 |
| | 1 |
| | (6 | ) | | (4 | ) | | (3 | ) | Net periodic benefit gain | | $ | (4 | ) | | $ | (5 | ) | | $ | (4 | ) | | $ | (4 | ) | | $ | (2 | ) | | $ | (1 | ) |
|
Schedule of Changes Recognized in Accumulated Other Comprehensive Income | | | | | | | | | | | | | | | | | | | | | | | | | | | Changes recognized in other comprehensive income, pretax: | | | | | | | | | | | | | Net actuarial gain (loss) | | $ | 4 |
| | $ | (5 | ) | | $ | (16 | ) | | $ | 5 |
| | $ | 7 |
| | $ | (3 | ) | Reclassification adjustments for amounts recognized in net periodic benefit cost | | 1 |
| | 1 |
| | 1 |
| | (6 | ) | | (4 | ) | | (3 | ) | Total gain (loss) recognized in other comprehensive income | | $ | 5 |
| | $ | (4 | ) | | $ | (15 | ) | | $ | (1 | ) | | $ | 3 |
| | $ | (6 | ) |
|
Schedule of Pre-Tax Amounts in Accumulated Other Comprehensive Income | Pre-tax amounts recognized in AOCI that have not yet been recognized as a component of net periodic benefit cost consist of the following: Table 15.3: Amounts Recognized in AOCI | | | | | | | | | | | | | | | | | | | | December 31, | | | 2016 | | 2015 | | 2016 | | 2015 | (Dollars in millions) | | Defined Pension
Benefits | | Other Postretirement
Benefits | Prior service cost | | $ | 0 |
| | $ | 0 |
| | $ | (2 | ) | | $ | (2 | ) | Net actuarial gain (loss) | | (66 | ) | | (71 | ) | | 12 |
| | 12 |
| Accumulated other comprehensive income (loss) | | $ | (66 | ) | | $ | (71 | ) | | $ | 10 |
| | $ | 10 |
|
|
Schedule of Pre-Tax Amount In Accumulated Other Comprehensive Income That Are Expected To Be Recognized Of Net Periodic Benefit Cost | Pre-tax amounts recorded in AOCI as of December 31, 2016 that are expected to be recognized as a component of our net periodic benefit cost in 2017 consist of the following: Table 15.4: Estimated Amortization of Unamortized Actuarial Gains and Losses - 2017 | | | | | | | | | | | | 2017 Estimate | (Dollars in millions) | | Defined
Pension
Benefits | | Other
Postretirement
Benefits | Prior service cost | | $ | 0 |
| | $ | 0 |
| Net actuarial gain (loss) | | (1 | ) | | 5 |
| Net gain (loss) | | $ | (1 | ) | | $ | 5 |
|
|
Schedule Of Weighted Average Assumptions Used in Accounting for Plans | The following table presents weighted-average assumptions used in the accounting for the plans: Table 15.5: Assumptions Used in the Accounting for the Plans | | | | | | | | | | | | | | | | December 31, | | | 2016 | | 2015 | | 2014 | | 2016 | | 2015 | | 2014 | | | Defined Pension
Benefits | | Other Postretirement
Benefits | Assumptions for benefit obligations at measurement date: | | | | | | | | | | | | | Discount rate | | 4.0% | | 4.2% | | 3.9% | | 4.0% | | 4.2% | | 3.9% | Assumptions for periodic benefit cost for the year ended: | | | | | | | | | | | | | Discount rate | | 4.2 | | 3.9 | | 4.6 | | 4.2 | | 3.9 | | 4.6 | Expected long-term rate of return on plan assets | | 6.5 | | 6.5 | | 6.5 | | 6.5 | | 6.5 | | 6.5 | Assumptions for year-end valuations: | | | | | | | | | | | | | Health care cost trend rate assumed for next year: | | | | | | | | | | | | | Pre-age 65 | | N/A | | N/A | | N/A | | 6.7 | | 7.0 | | 7.3 | Post-age 65 | | N/A | | N/A | | N/A | | 6.8 | | 7.1 | | 7.4 | Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) | | N/A | | N/A | | N/A | | 4.5 | | 4.5 | | 4.5 | Year the rate reaches the ultimate trend rate | | N/A | | N/A | | N/A | | 2037 | | 2037 | | 2028 |
|
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates | Assumed health care trend rates have a significant effect on the amounts reported for the other postretirement benefit plans. The following table presents the effect of a one-percent change in the assumed health care cost trend rate on our accumulated postretirement benefit obligation. There were insignificant effects on total service and interest cost for the years ended December 31, 2016, 2015 and 2014. Table 15.6: Sensitivity Analysis | | | | | | | | | | | | | | | | | | | | Year Ended December 31, | | | 2016 | | 2015 | (Dollars in millions) | | 1% Increase | | 1% Decrease | | 1% Increase | | 1% Decrease | Effect on year-end postretirement benefit obligation | | $ | 4 |
| | $ | (4 | ) | | $ | 5 |
| | $ | (4 | ) |
|
Schedule of Allocation of Plan Assets | Table 15.8: Plan Assets Measured at Fair Value on a Recurring Basis | | | | | | | | | | | | | | | | | | | | December 31, 2016 | | | Fair Value Measurements Using | | Assets at Fair Value | (Dollars in millions) | | Level 1 | | Level 2 | | Level 3 | | Plan assets, at fair value: | | | | | | | | | Corporate bonds (S&P rating of A or higher) | | $ | 0 |
| | $ | 15 |
| | $ | 0 |
| | $ | 15 |
| Corporate bonds (S&P rating of lower than A) | | 0 |
| | 29 |
| | 0 |
| | 29 |
| Government securities | | 0 |
| | 31 |
| | 0 |
| | 31 |
| Mortgage-backed securities | | 0 |
| | 11 |
| | 0 |
| | 11 |
| Municipal bonds | | 0 |
| | 1 |
| | 0 |
| | 1 |
| Money market fund | | 0 |
| | 2 |
| | 0 |
| | 2 |
| Plan assets in fair value hierarchy | | $ | 0 |
| | $ | 89 |
| | $ | 0 |
| | $ | 89 |
| Plan assets not classified in fair value hierarchy(1): | | | | | | | | | Common collective trusts | | | | | | | | 143 |
| Total plan assets, at fair value | | | | | | | | $ | 232 |
|
| | | | | | | | | | | | | | | | | | | | December 31, 2015 | | | Fair Value Measurements Using | | Assets at Fair Value | (Dollars in millions) | | Level 1 | | Level 2 | | Level 3 | | Plan assets, at fair value: | | | | | | | | | Corporate bonds (S&P rating of A or higher) | | $ | 0 |
| | $ | 15 |
| | $ | 0 |
| | $ | 15 |
| Corporate bonds (S&P rating of lower than A) | | 0 |
| | 30 |
| | 0 |
| | 30 |
| Government securities | | 0 |
| | 40 |
| | 0 |
| | 40 |
| Mortgage-backed securities | | 0 |
| | 12 |
| | 0 |
| | 12 |
| Municipal bonds | | 0 |
| | 1 |
| | 0 |
| | 1 |
| Plan assets in fair value hierarchy | | $ | 0 |
| | $ | 98 |
| | $ | 0 |
| | $ | 98 |
| Plan assets not classified in fair value hierarchy(1): | | | | | | | | | Common collective trusts | | | | | | | | 129 |
| Total plan assets, at fair value | | | | | | | | $ | 227 |
|
| | (1) | These plan assets are measured at net asset value per share (or its equivalent) as practical expedient and have not been classified in the fair value hierarchy. The fair value amounts are presented in this table to reconcile to the line items presented in Table 15.1: Changes in Benefit Obligation and Plan Assets. |
The asset allocations as of the annual measurement dates are as follows: Table 15.7: Plan Assets | | | | | | | | December 31, | | | 2016 | | 2015 | Common collective trusts(1) | | 62% | | 57% | Corporate bonds (Standard & Poor’s (“S&P”) rating of A or higher) | | 6 | | 6 | Corporate bonds (S&P rating of lower than A) | | 12 | | 13 | Government securities | | 13 | | 18 | Mortgage-backed securities | | 5 | | 5 | Municipal bonds | | 1 | | 1 | Money market fund | | 1 | | 0 | Total | | 100% | | 100% |
| | (1) | Common collective trusts primarily include domestic and international equity securities. |
|
Schedule of Expected Future Benefit Payments | The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Table 15.9: Expected Future Benefits Payments | | | | | | | | | | (Dollars in millions) | | Pension
Benefits | | Postretirement
Benefits | 2017 | | $ | 12 |
| | $ | 3 |
| 2018 | | 12 |
| | 3 |
| 2019 | | 12 |
| | 3 |
| 2020 | | 11 |
| | 3 |
| 2021 | | 11 |
| | 3 |
| 2022-2026 | | 52 |
| | 11 |
|
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