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Regulatory Matters Regulatory Matters - Annual Electric Distribution/Transmission Filings (Details) - USD ($) $ in Millions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 Months Ended
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Jan. 15, 2019 | Dec. 04, 2018 | Nov. 19, 2018 | Sep. 07, 2018 | Aug. 21, 2018 | Jun. 27, 2018 | May 31, 2018 | Apr. 20, 2018 | [4] | Apr. 17, 2018 | Apr. 16, 2018 | Mar. 08, 2018 | [4] | Mar. 02, 2018 | Feb. 09, 2018 | Feb. 06, 2018 | Jan. 31, 2018 | Jan. 18, 2018 | Dec. 19, 2017 | Dec. 18, 2017 | Nov. 16, 2017 | Dec. 31, 2018 | Dec. 31, 2017
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (44) |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 201 |  |  |  |  |
Prior Year Revenue Adjustment | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18 |
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55.00% |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [1],[2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (26) |
Public Utilities, Approved Equity Capital Structure, Percentage | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.32% |
Public Utilities, Approved Return on Equity, Percentage | [1],[3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11.50% |
Commonwealth Edison Co [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (58) |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [4] |  | $ (24) |  |  |  |  |  |  |  |  | $ (23) |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.52% |
Public Utilities, Requested Equity Capital Structure, Percentage |  |  | 8.69% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commonwealth Edison Co [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69 |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |
Prior Year Revenue Adjustment | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |
Proposed Capital Expenditure |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [1],[2],[5] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 26 |
Public Utilities, Approved Equity Capital Structure, Percentage | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.61% |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 72 |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18 |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |
Prior Year Revenue Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8 |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.82% |
Public Utilities, Approved Return on Equity, Percentage | [3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |
Potomac Electric Power Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  | $ 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 66 |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 39 |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  |  |  | $ 4 |  |  |  | $ (15) | $ (24) | [4] |  | $ 3 |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  | 10.30% |  |  |  |  |  | 9.50% |  | 9.525% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potomac Electric Power Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 13 |
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14 |
Prior Year Revenue Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13 |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27 |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.29% |
Public Utilities, Approved Return on Equity, Percentage | [3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |
Delmarva Power & Light Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [4] |  |  |  |  |  | $ (7) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 19 |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 13 |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12 | [4] |  |  |  |  |  | $ 19 |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.50% |  |  |
Public Utilities, Requested Return on Equity, Percentage |  |  |  |  |  |  | 9.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Delmarva Power & Light Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12 |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  | $ 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 23 |  |  |  |  |  |  |  |  |  |
Prior Year Revenue Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (4) |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.02% |
Public Utilities, Approved Return on Equity, Percentage | [3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |
Atlantic City Electric Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [6] |  |  | $ 122 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  |  |  |  |  | 10.10% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Atlantic City Electric Company [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Savings From Tax Cuts and Jobs Act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 11 |
[1] | The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted.
[2] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MzY0MUFFQzNGNTE3Mzk3OTI2RjIxNTRFRUQyNkYyMzMM}
[3] | As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO.
[4] | Includes the annual ongoing TCJA tax savings further discussed below.
[5] | BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $12 million to recover the costs of providing transmission service to specifically designated load by BGE.
[6] | {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NUYyM0EwMDI1MDhGQUUyMUZEMzExNTNGOUY0NjExNDUM}

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