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Early Plant Retirements Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Oct. 01, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Property, Plant and Equipment [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  | $ 154 | $ 208 | $ 6,923
Exelon Generation Co L L C [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  | $ 154 | $ 208 | $ 293
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Ownership interest |  | 42.59% |  |
Everett Marine Terminal [Member] | Exelon Generation Co L L C [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross | $ 81 |  |  |
Business Combination, Separately Recognized Transactions, Net Gains and Losses | $ 75 |  |  |

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- Definition The net gains or losses recognized for each transaction with the acquiree that was recognized separately from the acquisition of assets and assumptions of liabilities in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 + Details
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