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Goodwill and Other Intangibles - Narrative (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2006 USD ($)
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | $ 539,000,000 | $ 539,000,000 | $ 662,000,000 |  |
Goodwill deductible for U.S. income tax purposes | 460,000,000 | 460,000,000 | 547,000,000 |  |
Impairment |  | 26,000,000 | 64,000,000 |  |
Emission allowances held-for-sale | 9,000,000 | 9,000,000 |  |  |
Out-of-market contracts, net | 207,000,000 | 207,000,000 | 230,000,000 |  |
Accumulated amortization, out of market contracts | 358,000,000 | 358,000,000 | 457,000,000 |  |
Emission Allowances |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Impairment |  | 20,000,000 | 23,000,000 |  |
PPA |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Impairment |  | 6,000,000 | $ 0 |  |
Impairment related to power purchase agreements |  | 6,000,000 |  |  |
Texas Genco |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill in connection with acquisition |  |  |  |  | $ 1,700,000,000
EME Project Financings | Lease Agreements |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Out-of-market contracts, net | 159,000,000 | 159,000,000 |  |  |
SPP |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | 0 | 0 |  |  |
Goodwill, Impairment Loss | 12,000,000 |  |  |  |
BETM | Held-for-sale |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | 21,000,000 | 21,000,000 |  |  |
Goodwill, Impairment Loss | $ 90,000,000 |  |  |  |
Texas |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill, Impairment Loss |  | $ 337,000,000 |  | $ 1,400,000,000 |
Percentage of carrying amount | 0.43 | 0.43 |  |  |
EME Project Financings |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | $ 165,000,000 | $ 165,000,000 |  |  |
Out-of-market contracts, net |  |  |  | $ 159,000,000 |
Retail |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | 341,000,000 | 341,000,000 |  |  |
Other |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | 33,000,000 | 33,000,000 |  |  |
Texas |  |  |  |  |
Goodwill and Other Intangibles |  |  |  |  |
Goodwill | $ 0 | $ 0 |  |  |

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- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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