Regulatory Matters Annual Electric Distribution Filings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 138	$ (50)	$ 269
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 90,000,000	$ 68,000,000	$ 36,000,000
Public Utilities, Requested Equity Capital Structure, Percentage		8.47%	8.61%	8.62%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ 4,000,000	$ 18,000,000	$ (14,000,000)
Public Utilities, Approved Rate Increase (Decrease), Amount		94,000,000	$ 86,000,000	$ 22,000,000
Public Utilities, Requested Return on Equity, Percentage			11.50%	11.50%
Electric Distribution [Member] | Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 134	$ 85	$ 160
Public Utilities, Requested Equity Capital Structure, Percentage		6.71%	7.05%	7.06%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ (18,000,000)	$ 127	$ (67)	$ 232
Public Utilities, Approved Equity Capital Structure, Percentage		6.69%	7.02%	7.04%
Public Utilities, Approved Rate Increase (Decrease), Amount		$ (7)	$ (152)	$ 72
Public Utilities, Approved Return on Equity, Percentage		8.59%	9.09%	9.20%
Public Utilities, Requested Return on Equity, Percentage		8.64%	9.14%	9.25%