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Variable Interest Entities Variable Interest Entities - Narrative (Details) $ in Millions | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jul. 31, 2017 USD ($) | Nov. 30, 2015 | Jun. 30, 2015 | Jul. 30, 2014 | Dec. 31, 2018 USD ($) VIE project | Dec. 31, 2017 USD ($) VIE | Dec. 31, 2016 USD ($) | Jul. 18, 2014 USD ($) | Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Number of variable interest entities consolidated | VIE |  |  |  |  | 5 | 5 |  |  |
Number of variable interest entities not consolidated by equity holders | VIE |  |  |  |  | 7 | 7 |  |  |
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net |  |  |  |  | $ 15 |  |  |  |
Guarantee obligations maximum exposure |  |  |  |  | 61 |  |  |  |
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount |  |  |  |  | 15 |  |  |  |
2015 ESA Investco, LLC [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  | 99.00% |  |  |  |  |  |
Payment Guarantee [Member] | CENG [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Guarantee obligations maximum exposure |  |  |  |  |  |  |  |  | $ 245
Financial Guarantee [Member] | CENG [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Guarantee obligations maximum exposure |  |  |  |  |  |  |  |  | 165
Equity interest member [Member] | 2015 ESA Investco, LLC [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  | 90.00% |  |  |  |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net |  |  |  |  | 13 |  |  |  |
Parental guarantee provided |  |  |  |  | $ 34 |  |  |  |
Ownership Percentage Of Consolidated Variable Interest Entities |  |  |  |  | 62.00% |  |  |  |
Wind project entities with noncontrolling equity interests | project |  |  |  |  | 4 |  |  |  |
Noncontrolling equity interest ownership percentage held by third parties |  |  |  |  | 1.00% |  |  |  |
Number of projects with significant economic power | project |  |  |  |  | 3 |  |  |  |
Ownership interests in project entities |  |  |  |  | 99.00% |  |  |  |
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount |  |  |  |  | $ 13 |  |  |  |
Exelon Generation Co L L C [Member] | ExGen Renewables Holdings, LLC [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from Sale of Interest in Partnership Unit | $ 400 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  |  |  | 100.00% |  |  |  |
Ownership Percentage Of Consolidated Variable Interest Entities |  |  |  |  | 100.00% |  |  |  |
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Parental guarantee provided |  |  |  |  | $ 275 |  |  |  |
Exelon Generation Co L L C [Member] | CENG [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Parental guarantee provided |  |  |  |  | $ 688 |  |  |  |
Ownership interest |  |  |  |  | 50.01% |  |  |  |
Due from Affiliates |  |  |  |  | $ 196 |  |  |  | $ 400
Exelon Generation Co L L C [Member] | Distributed Energy Company [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  |  | 90.00% |  |  |  |  |
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests |  |  |  |  | 227 |  |  | $ 85 |
Exelon Generation Co L L C [Member] | Equity interest member [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  | 69.00% |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Equity interest member [Member] | ExGen Renewables Holdings, LLC [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 49.00% |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Equity interest member [Member] | Distributed Energy Company [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  |  | 90.00% |  |  |  |  |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Guarantee obligations maximum exposure |  |  |  |  | 16 |  |  |  |
Atlantic City Electric Company [Member] | ATF [Member] |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |
Cash Remitted To VIE |  |  |  |  | $ 30 | $ 48 | $ 60 |  |

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