Income Taxes - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2009	Dec. 31, 2014
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities	$ 345,000,000
Deferred tax gain under involuntary conversion provisions of the IRC				1,200,000,000
IRS asserted penalties for understatement of tax	90,000,000
Expected non-cash charge to earnings			265,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	810,000,000
Early termination amount		335,000,000
Taxes Payable, Current		285,000,000
Parent Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	1,282,000,000				1,829,000,000
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	733,000,000				1,357,000,000
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	147,000,000				149,000,000
Expected non-cash charge to earnings			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	310,000,000
Taxes Payable, Current		155,000,000
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	0				44,000,000
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	$ 120,000,000				$ 0