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Goodwill and Other Intangibles - Schedule of Amortization Expense (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | $ 207 | $ 231 | $ 238
Emission Allowances |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 73 | 66 | 60
Energy Supply |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 0 | 7 | 5
Fuel |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 1 | 2 | 2
Customer |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 1 | 2 | 2
Customer Relationships |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 35 | 49 | 67
Marketing Partnerships |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 5 | 8 | 14
Trade Names |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 23 | 22 | 23
PPA |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | 62 | 64 | 51
Other |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization of Intangible Assets | $ 7 | $ 11 | $ 14

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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