Income Taxes - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended				6 Months Ended
	Jul. 28, 2015	Sep. 30, 2014	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2013	Jun. 30, 2015	Jun. 30, 2014	Jul. 20, 2015	Dec. 31, 2014	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			$ 1,289				$ 1,289			$ 1,829
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions				$ 661
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities							347
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			810				810
Early termination amount					$ 335
Unrecognized Tax Benefits, Interest on Income Taxes Accrued						265
Income taxes			327		277		690	$ 224
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			395				395
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			745				745			1,357
Unrecognized tax benefits that if recognized would affect the effective tax rate			227				227
Increase (Decrease) in Income Taxes		$ 227
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount			120
Income taxes			181		199		407	(1)
Exelon Generation Co L L C [Member] | Settlement with Taxing Authority [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Expected non-cash charge to earnings									$ 21
Unrecognized Tax Benefits, Interest on Income Taxes Accrued									$ 21
Income taxes	$ 45
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			146				146			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			310				310
Unrecognized Tax Benefits, Interest on Income Taxes Accrued						$ 170
Income taxes			68		72		127	137
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			145				145
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			0				0			44
Income taxes			27		23		85	57
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			120				120			$ 0
Income taxes			$ 32		$ 14		$ 105	$ 72