Income Taxes - Narrative (Details) (USD $)	3 Months Ended	9 Months Ended					1 Months Ended	3 Months Ended		3 Months Ended								9 Months Ended
	Mar. 31, 2014	Sep. 30, 2014	Mar. 31, 2013	Dec. 31, 2009	Sep. 30, 2014 Parent Company [Member]	Dec. 31, 2013 Parent Company [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2014 Commonwealth Edison Co [Member]	Mar. 31, 2014 Commonwealth Edison Co [Member]	Dec. 31, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2014 PECO Energy Co [Member]	Dec. 31, 2013 PECO Energy Co [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member]	Dec. 31, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate					$ 1,808,000,000	$ 2,175,000,000	$ 1,342,000,000	$ 1,342,000,000	$ 1,415,000,000		$ 151,000,000		$ 324,000,000	$ 44,000,000	$ 44,000,000	$ 0	$ 0
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		180,000,000
Increase (Decrease) in Income Taxes							75,000,000
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount								90,000,000
Deferred tax gain under involuntary conversion provisions of the IRC				1,200,000,000
IRS asserted penalties for understatement of tax		87,000,000
Expected non-cash charge to earnings			265,000,000							170,000,000
Non-cash equity contributions										172,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		800,000,000									310,000,000
Early termination amount	335,000,000
Taxes Payable, Current	285,000,000											155,000,000
Cash tax benefit (detriment) as a result of repair costs deduction																		$ 100,000,000	$ 120,000,000