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Regulatory Assets and Liabilities (Tables) | 12 Months Ended
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Dec. 31, 2016
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets and Liabilities [Table Text Block] | Regulatory assets and liabilities consist of the following (dollars in millions):
| Weighted Average Remaining Life (1) |  | As of December 31,
| 2016 |  | 2015
| Current |  | Noncurrent |  | Current |  | Noncurrent
Regulatory assets: |  |  |  |  |  |  |  |  |
Price risk management (2) | 6 years |  | $ | 26 |  |  | $ | 120 |  |  | $ | 120 |  |  | $ | 161 |
Pension and other postretirement plans (2) | (3) |  | — |  |  | 235 |  |  | — |  |  | 239 |
Deferred income taxes (2) | (4) |  | — |  |  | 86 |  |  | — |  |  | 86 |
Debt issuance costs (2) | 6 years |  | — |  |  | 22 |  |  | — |  |  | 16 |
Other (5) | Various |  | 10 |  |  | 35 |  |  | 9 |  |  | 22 |
Total regulatory assets |  |  | $ | 36 |  |  | $ | 498 |  |  | $ | 129 |  |  | $ | 524 |
Regulatory liabilities: |  |  |  |  |  |  |  |  |
Asset retirement removal costs (6) | (4) |  | $ | — |  |  | $ | 887 |  |  | $ | — |  |  | $ | 837 |
Trojan decommissioning activities | 3 years |  | 18 |  |  | — |  |  | 17 |  |  | 15 |
Asset retirement obligations (6) | (4) |  | — |  |  | 49 |  |  | — |  |  | 45 |
Other | Various |  | 33 |  |  | 22 |  |  | 38 |  |  | 31 |
Total regulatory liabilities |  |  | $ | 51 |  | (7) | $ | 958 |  |  | $ | 55 |  | (7) | $ | 928 |
(1) | As of December 31, 2016.
(2) | Does not include a return on investment.
(3) | Recovery expected over the average service life of employees.
(4) | Recovery expected over the estimated lives of the assets.
(5) | Of the total other unamortized regulatory asset balances, a return is recorded on $44 million and $29 million as of December 31, 2016 and 2015, respectively.
(6) | Included in rate base for ratemaking purposes.
(7) | Included in Accrued expenses and other current liabilities on the consolidated balance sheets.

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- Definition Tabular disclosure of assets and liabilities that are created in connection with regulatory accounting [Table Text Block] + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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