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Regulatory Matters Regulatory Matters - Schedule of TCJA Savings (Details) - USD ($) $ in Millions |  |  |  |  |  |  |  |  |  |  |  |  | 3 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 07, 2018 | Aug. 29, 2018 | Jul. 01, 2018 | Jun. 27, 2018 | Apr. 20, 2018 | Mar. 29, 2018 | Mar. 02, 2018 | Feb. 09, 2018 | Feb. 06, 2018 | Feb. 05, 2018 | Jan. 31, 2018 | Jan. 18, 2018 | Sep. 30, 2018
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  | $ 201 |
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  | $ 71 |  |  |  |  |  |  |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  | $ 23 |  |  |  |  |  |
Gas Distribution [Member] | PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  | $ 4 |  |  |  |  |  |  |  |  |  |
Gas Distribution [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  | $ 31 |  |
Public Utilities, Rate Credit |  |  |  |  |  |  |  |  |  |  | 2 |  |
Gas Distribution [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  | $ 7 |  |  |  |  |
Public Utilities, Rate Credit | $ 1 |  |  |  |  |  |  |  |  |  |  |  |
Electric Distribution [Member] | PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Rate Credit |  |  |  |  |  |  |  |  |  |  | 67 |  |
Electric Distribution [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  | $ 72 |  |
Electric Distribution [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  | $ 19 |  |  |  |  |
Public Utilities, Rate Credit |  |  |  | $ 3 |  |  |  |  |  |  |  |  |
Electric Distribution [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  | $ 39 |  |  |  |
Public Utilities, Rate Credit | $ 20 |  |  |  | $ 10 |  |  |  |  |  |  |  |
Electric Distribution [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Rate Credit |  | $ 6 |  |  |  |  |  |  |  |  |  |  |
Maryland Service Territory [Member] | Electric Distribution [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Schedule of TCJA Savings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  | $ 31 |  |  | $ 14
Public Utilities, Rate Credit |  |  |  |  |  |  |  |  |  |  |  |  | $ 2

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