Significant Accounting Policies Balance Sheet Classification of Deferred Taxes (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Other noncurrent assets	$ 1,445,000,000	$ 923,000,000
Other noncurrent liabilities	1,491,000,000	2,147,000,000
New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(244)
Other noncurrent assets	3
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(241)
Commonwealth Edison Co [Member]
Other noncurrent assets	324,000,000	237,000,000
Other noncurrent liabilities	507,000,000	889,000,000
Commonwealth Edison Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	0
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	(63)
Other noncurrent liabilities	63
Exelon Generation Co L L C [Member]
Other noncurrent assets	627,000,000	578,000,000
Other noncurrent liabilities	602,000,000	719,000,000
Exelon Generation Co L L C [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(327)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(327)
PECO Energy Co [Member]
Other noncurrent assets	21,000,000	20,000,000
Other noncurrent liabilities	90,000,000	95,000,000
PECO Energy Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(69)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(69)
Baltimore Gas and Electric Company [Member]
Other noncurrent assets	8,000,000	9,000,000
Other noncurrent liabilities	61,000,000	$ 60,000,000
Baltimore Gas and Electric Company [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(6)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	(52)
Other noncurrent liabilities	$ 46