Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	100.00%
Third Party interest in ComEd (less than $1 million)	$ 1,775,000,000	$ 1,308,000,000
Minimum expectation of tax position to be realized	50.00%
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
Third Party interest in ComEd (less than $1 million)	$ 1,000,000	1,000,000
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	$ (0.001)
Development Costs, Period Cost	1,700,000,000	1,300,000,000
Utilities Operating Expense, Other	$ 13,000,000
Potomac Electric Power Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		4,000,000	$ 1,000,000
Delmarva Power and Light Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		1,000,000
Atlantic City Electric Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				$ 12,000,000
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results		2,000,000	$ 1,000,000
Pepco Holdings LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 34,000,000
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.00%