Regulatory Matters Regulatory Matters - Schedule of Revenue Increases (Decreases) (Details) - Commonwealth Edison Co [Member] - USD ($) $ in Millions				12 Months Ended
	Sep. 11, 2017	Jun. 09, 2017	[1]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Public Utilities, Requested Rate Increase (Decrease), Amount		$ (7)		$ 44	[2]	$ 90	[2]	$ 68	[2]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 12			$ 11	[2]	$ 94	[2]	$ 86	[2]
Public Utilities, Approved Equity Capital Structure, Percentage	6.47%			8.43%	[3]	8.47%	[3]	8.61%	[3]
Public Utilities, Approved Return on Equity, Percentage	8.40%

[1] Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs.

[2] The time period for any challenges to the annual transmission formula rate update flings expired with no challenges submitted

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