Income Taxes - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended				9 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Mar. 31, 2013	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		$ 1,204				$ 1,204		$ 1,829
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities						261
Deferred tax gain under involuntary conversion provisions of the IRC										$ 1,200
IRS asserted penalties for understatement of tax						90
Expected non-cash charge to earnings									$ 265
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		560				560
Early termination amount				$ 335
Unrecognized Tax Benefits, Interest on Income Taxes Accrued									265
Income taxes		115		422		805	$ 646
Increase in Unrecognized Tax Benefits is Reasonably Possible		71				71
Settlement with Taxing Authority [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		394				394
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		660				660		1,357
Unrecognized tax benefits that if recognized would affect the effective tax rate		141				141
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions			$ 661
Increase (Decrease) in Income Taxes	$ 141
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount		120
Income taxes		(36)		291		371	290
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		144				144		149
Expected non-cash charge to earnings									170
Non-cash equity contributions					$ 172
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		165				165
Unrecognized Tax Benefits, Interest on Income Taxes Accrued									$ 170
Income taxes		99		84		226	221
Increase in Unrecognized Tax Benefits is Reasonably Possible		11				11
Commonwealth Edison Co [Member] | Settlement with Taxing Authority [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		144				144
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		0				0		44
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions			$ 43
Income taxes		37		25		122	82
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits		120				120		$ 0
Income taxes		$ 35		$ 31		$ 141	$ 103