Income Taxes (Details) (USD $)	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2010
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%	[1]	35.00%		35.00%	[1]	35.00%
Increase (decrease) due to:
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	3.50%	[1]	2.00%		(10.70%)	[1]	3.90%
Effective Income Tax Rate Reconciliation Qualified Nuclear Decommissioning Trust Fund Income Losses	(2.00%)	[1]	1.30%		6.30%	[1]	1.80%
Effective Income Tax Rate Reconciliation, Deductions, Qualified Production Activities	0.70%	[1]	(1.00%)		(0.20%)	[1]	(1.00%)
Effective Income Tax Rate Reconciliation, Tax Exempt Income	(0.40%)	[1]	(0.20%)		(0.40%)	[1]	(0.10%)
Effective Income Tax Rate Reconciliation Nontaxable Postretirement Benefits			0.00%
Effective Income Tax Rate Reconciliation Elimination Of Deductions Medicare Prescription Drug Benefit	0.30%	[1]			0.20%	[1]	0.00%
Effective Income Tax Rate Reconciliation, Tax Credits, Investment	(0.70%)	[1]	(0.20%)		(0.70%)	[1]	(0.20%)
Effective Income Tax Rate Reconciliation Plant Basis Differences	(0.70%)	[1]	0.00%		(0.60%)	[1]	0.00%
Effective Income Tax Rate Reconciliation Deductions Other	(2.20%)	[1]	(0.90%)		(2.60%)	[1]	(0.90%)
Effective Income Tax Rate Reconciliation Fines And Penalties	0.00%	[1]			6.10%	[1]
Effective Income Tax Rate Reconciliation Merger Expenses	(0.80%)	[1],[2]			5.60%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments	(2.30%)	[1]	(1.10%)		(1.30%)	[1]	(0.80%)
Effective income tax rate	30.40%	[1]	34.90%		36.70%	[1]	37.70%
Unrecognized Tax Benefits For Which Timing Of Ultimate Benefits Uncertain [Abstract]
Tax positions for which there is uncertainty about the timing of tax benefits	$ 1,050,000,000				$ 1,050,000,000
1999 Sale of Fossil Generating Assets [Abstract]
Deferred tax gain on sale of fossil generating assets	2,800,000,000				2,800,000,000
Deferred tax gain under involuntary conversion provisions of the IRC	1,600,000,000				1,600,000,000
Deferred tax gain under like-kind exchange provisions of the IRC	1,200,000,000				1,200,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	860,000,000				860,000,000
Potential interest expense from a successful IRS challenge of the like-kind exchange position	260,000,000				260,000,000
IRS withdrawn penalties originally asserted for understatement of tax related to involuntary conversion					110,000,000
IRS asserted penalties for understatement of tax related to like-kind exchange					86,000,000
Tax Settlement [Abstract]
Tax and interest to be assessed under preliminary settlement with IRS within the next 12 months	300,000,000				300,000,000
Refund due from the settlement of the 2001 tax method of accounting change for certain overhead costs under SSCM	300,000,000				300,000,000
Payment to IRS for open tax positions									302,000,000
Income tax benefit recorded as a result of re-apportionment of state income taxes [Abstract]
Income tax benefit recorded as a result of re-apportionment of state income taxes					72,000,000
Gross Deferred Income tax benefit recorded as a result of re-apportionment of state income taxes					116,000,000
Gross Deferred Income tax expense recorded as a result of re-apportionment of state income taxes					44,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	126,000,000		332,000,000		284,000,000		779,000,000
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%	[1]	35.00%		35.00%	[1]	35.00%
Increase (decrease) due to:
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	2.30%	[1]	3.00%		1.60%	[1]	4.70%
Effective Income Tax Rate Reconciliation Qualified Nuclear Decommissioning Trust Fund Income Losses	(3.80%)	[1]	1.90%		8.00%	[1]	2.60%
Effective Income Tax Rate Reconciliation, Deductions, Qualified Production Activities	1.60%	[1]	(1.50%)		(0.20%)	[1]	(1.40%)
Effective Income Tax Rate Reconciliation, Tax Exempt Income	(0.80%)	[1]	(0.20%)		(0.50%)	[1]	(0.20%)
Effective Income Tax Rate Reconciliation Nontaxable Postretirement Benefits			0.00%
Effective Income Tax Rate Reconciliation Elimination Of Deductions Medicare Prescription Drug Benefit	0.00%	[1]			0.00%	[1]	0.00%
Effective Income Tax Rate Reconciliation, Tax Credits, Investment	(0.70%)	[1]	(0.20%)		(0.60%)	[1]	(0.20%)
Effective Income Tax Rate Reconciliation Plant Basis Differences	0.00%	[1]	0.00%		0.00%	[1]	0.00%
Effective Income Tax Rate Reconciliation Deductions Other	(4.00%)	[1]	(1.50%)		(3.40%)	[1]	(1.30%)
Effective Income Tax Rate Reconciliation Fines And Penalties	0.00%	[1]			7.60%	[1]
Effective Income Tax Rate Reconciliation Merger Expenses	0.00%	[1],[2]			0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments	(3.60%)	[1]	(1.80%)		(1.00%)	[1]	(1.40%)
Effective income tax rate	26.00%	[1]	34.70%		46.50%	[1]	37.80%
Unrecognized Tax Benefits For Which Timing Of Ultimate Benefits Uncertain [Abstract]
Tax positions for which there is uncertainty about the timing of tax benefits	885,000,000				885,000,000
Tax Settlement [Abstract]
Refunds expected to be received (paid) as a result of preliminary settlement with IRS	(10,000,000)				(10,000,000)
Income tax benefit recorded as a result of re-apportionment of state income taxes [Abstract]
Gross Deferred Income tax benefit recorded as a result of re-apportionment of state income taxes					14,000,000
Gross Deferred Income tax expense recorded as a result of re-apportionment of state income taxes					14,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	58,000,000		235,000,000		289,000,000		571,000,000
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%		35.00%		35.00%		35.00%
Increase (decrease) due to:
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	5.20%		3.20%		5.70%		4.90%
Effective Income Tax Rate Reconciliation Qualified Nuclear Decommissioning Trust Fund Income Losses	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Deductions, Qualified Production Activities	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Exempt Income	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation Nontaxable Postretirement Benefits			(4.80%)
Effective Income Tax Rate Reconciliation Elimination Of Deductions Medicare Prescription Drug Benefit	1.00%				0.60%		(2.80%)
Effective Income Tax Rate Reconciliation, Tax Credits, Investment	(0.80%)		(0.40%)		(0.50%)		(0.40%)
Effective Income Tax Rate Reconciliation Plant Basis Differences	0.10%		0.20%		0.00%		(0.10%)
Effective Income Tax Rate Reconciliation Deductions Other	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation Fines And Penalties	0.00%				0.00%
Effective Income Tax Rate Reconciliation Merger Expenses	0.00%	[2]			0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments	0.30%		0.50%		0.30%		0.30%
Effective income tax rate	40.80%		33.70%		41.10%		36.90%
Unrecognized Tax Benefits For Which Timing Of Ultimate Benefits Uncertain [Abstract]
Tax positions for which there is uncertainty about the timing of tax benefits	68,000,000				68,000,000
1999 Sale of Fossil Generating Assets [Abstract]
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	510,000,000				510,000,000
Potential interest expense from a successful IRS challenge of the like-kind exchange position	160,000,000				160,000,000
Tax Settlement [Abstract]
Refunds expected to be received (paid) as a result of preliminary settlement with IRS	(405,000,000)				(405,000,000)
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	29,000,000		58,000,000		90,000,000		107,000,000
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%		35.00%		35.00%		35.00%
Increase (decrease) due to:
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	3.10%		1.50%		3.30%		(1.60%)
Effective Income Tax Rate Reconciliation Qualified Nuclear Decommissioning Trust Fund Income Losses	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Deductions, Qualified Production Activities	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Exempt Income	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation Nontaxable Postretirement Benefits			0.00%
Effective Income Tax Rate Reconciliation Elimination Of Deductions Medicare Prescription Drug Benefit	0.00%				0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Credits, Investment	(0.30%)		(0.30%)		(0.30%)		(0.30%)
Effective Income Tax Rate Reconciliation Plant Basis Differences	(3.60%)		(0.10%)		(3.60%)		(0.20%)
Effective Income Tax Rate Reconciliation Deductions Other	0.00%		0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation Fines And Penalties	0.00%				0.00%
Effective Income Tax Rate Reconciliation Merger Expenses	0.00%	[2]			0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments	0.20%		0.10%		0.00%		(0.20%)
Effective income tax rate	34.40%		36.20%		34.40%		32.70%
Unrecognized Tax Benefits For Which Timing Of Ultimate Benefits Uncertain [Abstract]
Tax positions for which there is uncertainty about the timing of tax benefits	48,000,000				48,000,000
Tax Settlement [Abstract]
Refunds expected to be received (paid) as a result of preliminary settlement with IRS	135,000,000				135,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	42,000,000		47,000,000		93,000,000		102,000,000
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%	[3]	35.00%	[3]	35.00%	[3]	35.00%	[3]
Increase (decrease) due to:
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	6.20%	[3]	5.20%	[3]	2.30%	[3]	4.70%	[3]
Effective Income Tax Rate Reconciliation Qualified Nuclear Decommissioning Trust Fund Income Losses	0.00%	[3]	0.00%	[3]	0.00%	[3]	0.00%	[3]
Effective Income Tax Rate Reconciliation, Deductions, Qualified Production Activities	0.00%	[3]	0.00%	[3]	0.00%	[3]	0.00%	[3]
Effective Income Tax Rate Reconciliation, Tax Exempt Income	0.00%	[3]	0.00%	[3]	0.00%	[3]	0.00%	[3]
Effective Income Tax Rate Reconciliation Elimination Of Deductions Medicare Prescription Drug Benefit	2.70%	[3]	2.80%	[3]	(3.10%)	[3]	(1.00%)	[3]
Effective Income Tax Rate Reconciliation, Tax Credits, Investment	(1.70%)	[3]	(0.90%)	[3]	3.80%	[3]	(0.30%)	[3]
Effective Income Tax Rate Reconciliation Plant Basis Differences	(4.70%)	[3]	(2.20%)	[3]	10.60%	[3]	(1.00%)	[3]
Effective Income Tax Rate Reconciliation Deductions Other	0.00%	[3]	0.00%	[3]	0.00%	[3]	0.00%	[3]
Effective Income Tax Rate Reconciliation Fines And Penalties	0.00%	[3]			0.00%	[3]
Effective Income Tax Rate Reconciliation Merger Expenses	0.00%	[2],[3]			(18.30%)	[2],[3]
Effective Income Tax Rate Reconciliation, Other Adjustments	(1.50%)	[3]	3.00%	[3]	3.00%	[3]	0.00%	[3]
Effective income tax rate	36.00%	[3]	42.90%	[3]	33.30%	[3]	37.40%	[3]
Unrecognized Tax Benefits For Which Timing Of Ultimate Benefits Uncertain [Abstract]
Tax positions for which there is uncertainty about the timing of tax benefits	10,000,000				10,000,000
Interest recognized related to uncertain tax positions [Abstract]
Net interest (income) expense recognized related to uncertain tax positions	1,000,000				7,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	$ 9,000,000		$ 12,000,000		$ (7,000,000)		$ 58,000,000

[1] Exelon activity for the three and six months ended June 30, 2012 includes the results of Constellation and BGE for March 12, 2012 - June 30, 2012. Generation activity for the three and six months ended June 30, 2012 includes the results of Constellation for March 12, 2012 - June 30, 2012.

[2] Prior to the close of the merger, the Registrants recorded the applicable taxes on merger transaction costs assuming the merger would not be completed. Upon closing of the merger, the Registrants reversed such taxes for those merger transaction costs that were determined to be non tax-deductible upon successful completion of a merger.

[3] BGE activity represents the activity for the three and six months ended June 30, 2012 and 2011. BGE recognized a loss before income taxes for the six months ended June 30, 2012. As a result, positive percentages represent an income tax benefit for BGE for the six months ended June 30, 2012.