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Regulatory Matters Regulatory Matters - Schedule of Completed Rate Cases (Details) - USD ($) $ in Millions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 Months Ended | 60 Months Ended
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Jan. 15, 2019 | Jan. 04, 2019 | Dec. 20, 2018 | Dec. 04, 2018 | Sep. 07, 2018 | Jun. 27, 2018 | Jun. 08, 2018 | May 31, 2018 | Apr. 20, 2018 | [4] | Apr. 17, 2018 | Apr. 16, 2018 | Mar. 29, 2018 | Mar. 08, 2018 | [4] | Feb. 09, 2018 | Dec. 19, 2017 | Dec. 18, 2017 | Nov. 16, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2023
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [1],[2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (26) |  |
Public Utilities, Approved Equity Capital Structure, Percentage | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.32% |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (44) |  |
Public Utilities, Approved Return on Equity, Percentage | [1],[3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11.50% |  |
Commonwealth Edison Co [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [4] |  |  |  | $ (24) |  |  |  |  |  |  |  | $ (23) |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34 |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.52% |  |
Public Utilities, Requested Equity Capital Structure, Percentage |  |  |  |  | 8.69% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (58) |  |
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 22 |  |
Public Utilities, Requested Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11.00% |  |
PECO Energy Co [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [4] |  |  | $ 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [4] |  |  |  |  |  |  |  |  |  |  |  |  | $ 82 |  |  |  |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [1],[2],[5] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 26 |  |
Public Utilities, Approved Equity Capital Structure, Percentage | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.61% |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10 |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  |
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  | $ 43 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  | $ 61 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  |  | 9.80% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8 |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.82% |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6 |  |
Public Utilities, Approved Return on Equity, Percentage | [3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  |
Potomac Electric Power Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  |  |  |  | $ 4 |  |  |  | $ (15) | $ (24) | [4] |  |  | $ 3 |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  | $ 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 66 |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  | 10.30% |  |  |  |  |  |  | 9.50% |  | 9.525% |  |  |  |  |  |  |  |  |  |  |  |
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27 |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.29% |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14 |  |
Public Utilities, Approved Return on Equity, Percentage | [3] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  |
Delmarva Power & Light Company [Member] | Electric Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12 | [4] |  |  | $ 19 |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 13 |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [4] |  |  |  |  |  | $ (7) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  |  |  |  |  |  | 9.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.50% |  |  |  |
Delmarva Power & Light Company [Member] | Gas Distribution [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | [4] |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4 |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | [4] |  |  |  |  | $ (4) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  |  |  |  |  | 9.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters Completed Rate Cases [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 200
[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.

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