Regulatory Matters Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions							12 Months Ended
		Jun. 15, 2018	Jun. 02, 2018	Mar. 02, 2018	Jan. 31, 2018	Jan. 18, 2018	Dec. 31, 2018
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase			$ 38
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 1
Tax Savings From Tax Cuts and Jobs Act						$ 201
Commonwealth Edison Co [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]						$ (44)
Annual reconciliation increase (decrease)							18
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]						$ (26)
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]						8.32%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]						11.50%
Commonwealth Edison Co [Member] | Electric Transmission [Member] | Subsequent Event [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]
Tax Savings From Tax Cuts and Jobs Act					$ 103
Baltimore Gas and Electric Company [Member] | Subsequent Event [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%
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act							$ 18
Potomac Electric Power Company [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]						6
Annual reconciliation increase (decrease)	[1],[2]						2
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] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act							$ 13
Delmarva Power and Light Company [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]						14
Annual reconciliation increase (decrease)	[1],[2]						13
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] | Subsequent Event [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
Tax Savings From Tax Cuts and Jobs Act				$ 23
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]						4
Annual reconciliation increase (decrease)	[1],[2]						(4)
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%
Atlantic City Electric Company [Member] | Electric Transmission [Member] | Subsequent Event [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.