Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 23,645,000,000	$ 19,212,000,000
Percentage ownership of consolidated subsidiaries	100.00%
Percentage ownership of common stock	100.00%
Third Party interest in ComEd (less than $1 million)	$ 1,308,000,000	1,332,000,000
Minimum expectation of tax position to be realized	50.00%
New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		157,000,000
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%
RITELine Illinois LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Third Party interest in ComEd (less than $1 million)	$ 1,000,000	1,000,000
Minority interest ownership percentage by parent	12.50%
Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 7,936,000,000	6,639,000,000
Third Party interest in ComEd (less than $1 million)	$ 1,307,000,000	1,333,000,000
Ownership interest upper bound	99.00%
Ownership interest	50.01%
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	$ (0.001)
Development costs expensed	22,000,000	13,000,000	$ 10,000,000
Exelon Generation Co L L C [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		70,000,000
Commonwealth Edison Co [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 5,844,000,000	5,665,000,000
Percentage ownership of consolidated subsidiaries	100.00%
Commonwealth Edison Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		34,000,000
Commonwealth Edison Co [Member] | RITELine Illinois LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	75.00%
Third-party percentage interest in subsidiaries	25.00%
PECO Energy Co [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 2,280,000,000	2,232,000,000
PECO Energy Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		14,000,000
Baltimore Gas and Electric Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 1,480,000,000	1,857,000,000
Baltimore Gas and Electric Company [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		$ 16,000,000
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%
Nuclear-Fuel Generating Facilities License Extension [Member] | Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Useful life	20 years