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Intangible Assets Renewable and Alternative Energy Credits (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2015
--- | --- | --- | ---
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Finite-Lived Intangible Assets, Gross |  | $ 1,267 | $ 1,228 |
Finite-Lived Intangible Assets, Accumulated Amortization |  | 1,149 | 1,255 |
Finite-Lived Intangible Assets, Net |  | 118 | (27) |
Exelon Generation Co L L C [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Exelon Generation Co L L C [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 270 | 312 |
Exelon Generation Co L L C [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 52 | 27 |
Exelon Consolidations [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 2 | 1 |
Exelon Consolidations [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 279 | 321 |
Exelon Consolidations [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 52 | 27 |
PECO Energy Co [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 2 | 1 |
PECO Energy Co [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
PECO Energy Co [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Pepco Holdings LLC [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Finite-Lived Intangible Assets, Gross |  |  |  | $ 25
Pepco Holdings LLC [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Pepco Holdings LLC [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 9 | 9 |
Pepco Holdings LLC [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Exelon Enterprise [Member] | Licensing Agreements [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Finite-Lived Intangible Assets, Gross | [1] | 95 | 95 |
Finite-Lived Intangible Assets, Accumulated Amortization | [1] | 34 | 25 |
Finite-Lived Intangible Assets, Net | [1] | 61 | 70 |
Delmarva Power & Light Company [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Delmarva Power & Light Company [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 8 | 8 |
Delmarva Power & Light Company [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Atlantic City Electric Company [Member] | Alternative energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 0 | 0 |
Atlantic City Electric Company [Member] | Renewable energy credit current [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | 1 | 1 |
Atlantic City Electric Company [Member] | Renewable energy credit noncurrent [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquired Finite-lived Intangible Asset, Residual Value |  | $ 0 | $ 0 |
[1] | (a)On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.

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- Definition The aggregate expected value at the end of their useful life of a major finite-lived intangible asset class acquired during the period either individually or as part of a group of assets (in either an asset acquisition or business combination). A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
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