Regulatory Matters Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions					3 Months Ended	9 Months Ended
		Sep. 11, 2017	Jun. 09, 2017	Feb. 01, 2017	Jun. 30, 2017	Sep. 30, 2017
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement increase			$ 7			$ 44	[1]
Annual reconciliation (decrease) increase	[1]					(33)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]					$ 11
Public Utilities, Approved Equity Capital Structure, Percentage		6.47%				8.43%	[1],[2]
Public Utilities, Approved Return on Equity, Percentage		8.40%				11.50%	[1],[3]
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement increase	[1]					$ 31
Annual reconciliation (decrease) increase	[1]					3
Proposed Capital Expenditure	[1],[4]					8
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]					$ 26
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2]					7.47%
Public Utilities, Approved Return on Equity, Percentage	[1],[3]					10.50%
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement increase	[1]					$ 5
Annual reconciliation (decrease) increase	[1]					15
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]					$ 20
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2]					7.92%
Public Utilities, Approved Return on Equity, Percentage	[1],[3]					10.50%
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement increase	[1]					$ 6
Annual reconciliation (decrease) increase	[1]					8
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]					$ 14
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2]					7.16%
Public Utilities, Approved Return on Equity, Percentage	[1],[3]					10.50%
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement increase	[1]					$ 20
Annual reconciliation (decrease) increase	[1]					22
Proposed Capital Expenditure				$ 29	$ 32
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]					$ 42
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2]					8.02%
Public Utilities, Approved Return on Equity, Percentage	[1],[3]					10.50%

[1] All rates are effective June 2017, subject to review by the FERC and other parties, which is due by fourth quarter 2017.

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

[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% 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.

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