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Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Goodwill [Roll Forward] |  |  |
Goodwill, Gross | $ 8,660 | $ 8,660 | $ 8,660
Goodwill, beginning balance | 6,677 | 6,677 |
Impairment losses | 0 | 0 |
Goodwill, ending balance | 6,677 | 6,677 |
Goodwill, Impaired, Accumulated Impairment Loss | 1,983 | 1,983 | 1,983
Exelon Generation Co L L C [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, beginning balance | 47 |  |
Goodwill, ending balance | 47 | 47 |
Commonwealth Edison Co [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Gross | 4,608 | 4,608 | 4,608
Goodwill, beginning balance | 2,625 | 2,625 |
Impairment losses | 0 | 0 |
Goodwill, ending balance | 2,625 | 2,625 |
Goodwill, Impaired, Accumulated Impairment Loss | 1,983 | 1,983 | 1,983
Delmarva Power & Light Company [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, beginning balance | 8 |  |
Goodwill, ending balance | 8 | 8 |
Pepco Holdings LLC [Member] |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Gross | 4,005 | 4,005 | $ 4,005
Goodwill, beginning balance | 4,005 | 4,005 |
Impairment losses | 0 |  |
Goodwill, ending balance | $ 4,005 | $ 4,005 |

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