Regulatory Matters Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions								9 Months Ended	12 Months Ended
		Aug. 21, 2018	Jun. 15, 2018	Jun. 02, 2018	Mar. 02, 2018	Jan. 31, 2018	Jan. 18, 2018	Sep. 30, 2018	Dec. 31, 2018
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase				$ 38					$ (44)	[1],[2]
Annual reconciliation increase (decrease)									18
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount				$ 1					$ (26)	[1],[2]
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								8.32%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]							11.50%
Tax Savings From Tax Cuts and Jobs Act							$ 201
Commonwealth Edison Co [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage								55.00%
Tax Savings From Tax Cuts and Jobs Act									$ 69
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]								10
Annual reconciliation increase (decrease)	[1],[2]								4
Proposed Capital Expenditure	[1],[2],[5]								12
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 26
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.61%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]							10.50%
Tax Savings From Tax Cuts and Jobs Act						$ 103
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]
Initial revenue requirement (decrease) increase	[1],[2]								6
Annual reconciliation increase (decrease)	[1],[2]								2
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 8
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.82%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
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 and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]								14
Annual reconciliation increase (decrease)	[1],[2]								13
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 27
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.29%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
Delmarva Power and 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]
Initial revenue requirement (decrease) increase		$ 40	$ 40						4	[1],[2]
Annual reconciliation increase (decrease)	[1],[2]								(4)
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 0
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								8.02%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
Tax Savings From Tax Cuts and Jobs Act					$ 23
Atlantic City Electric Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 11

[1] All rates are effective June 2018, subject to review by the FERC and other parties, which is due by fourth quarter 2018.

[2] The initial revenue requirement changes reflect the annual benefit of lower income tax rates effective January 1, 2018 resulting from the enactment of the TCJA of $69 million, $18 million, $13 million, $12 million and $11 million for ComEd, BGE, Pepco, DPL and ACE, respectively. They do not reflect the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. See further discussion above.

[3] Represents the weighted average debt and equity return on transmission rate bases.

[4] As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% 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 regional transmission organization.

[5] BGE's transmission revenues include a FERC-approved dedicated facilities charge to recover the costs of providing transmission service to a specifically designated load by BGE.