Income Taxes (Details) (USD $)	3 Months Ended					9 Months Ended				12 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Mar. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 1999
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%	[1]	35.00%			35.00%	[1]	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	3.00%	[1]	5.60%	[1]		5.30%	[1]	(4.70%)
Qualified nuclear decommissioning trust fund income (losses)	3.50%	[1]	7.80%	[1]		3.20%	[1]	6.90%
Domestic production activities deduction	0.00%	[1]	0.30%	[1]		0.00%	[1]
Tax exempt income	(0.20%)	[1]	(0.20%)	[1]		(0.20%)	[1]	(0.30%)
Nontaxable postretirement benefits			0.00%	[1]
Health Care Reform Legislation	0.10%	[1]				0.10%	[1]	0.20%
Amortization of investment tax credit	(1.50%)	[1]	(4.80%)	[1]		(2.30%)	[1]	(2.30%)
Plant basis differences	(0.80%)	[1]	(4.70%)	[1]		(1.70%)	[1]	(2.20%)
Production Tax Credits	(2.20%)	[1]	(2.50%)			(2.40%)	[1]	(2.60%)
Fines and Penalties								3.80%
Merger Expenses			(0.10%)					3.60%	[2]
Other	0.50%	[1]	(1.20%)			0.20%	[1]	(1.30%)
Effective income tax rate	37.40%	[1]	35.20%			37.20%	[1]	36.10%
Accounting for Uncertainty in Income Taxes [Abstract]
Unrecognized tax benefits that if recognized would affect the effective tax rate	$ 2,220,000,000					$ 2,220,000,000					$ 1,024,000,000
1999 Sale of Fossil Generating Assets [Abstract]
Deferred tax gain on sale of fossil generating assets												2,800,000,000
Deferred tax gain under involuntary conversion provisions of the IRC												1,600,000,000
Deferred tax gain under like-kind exchange provisions of the IRC												1,200,000,000
IRS asserted penalties for understatement of tax						265,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	840,000,000					840,000,000
IRS asserted penalties for understatement of tax related to like-kind exchange						87,000,000
FIN 48 Tax Remeasurement [Abstract]
FIN 48 Tax Remeasurement Interest Expense					65,000,000
Tax Settlement [Abstract]
Payment to IRS for open tax positions										302,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	439,000,000		161,000,000			733,000,000		445,000,000
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:
State income taxes, net of Federal income tax benefit	2.60%	[1]	5.90%	[1]		1.80%	[1]	2.50%
Qualified nuclear decommissioning trust fund income (losses)	5.30%	[1]	21.50%	[1]		5.10%	[1]	10.90%
Domestic production activities deduction	0.00%	[1]	0.80%	[1]		0.00%	[1]
Tax exempt income	(0.30%)	[1]	(0.50%)	[1]		(0.30%)	[1]	(0.50%)
Nontaxable postretirement benefits			0.00%
Health Care Reform Legislation	0.00%	[1]				0.00%	[1]	0.00%
Amortization of investment tax credit	(2.10%)	[1]	(13.00%)	[1]		(3.40%)	[1]	(3.30%)
Plant basis differences	0.00%	[1]	0.00%			0.00%	[1]	0.00%
Production Tax Credits	(3.30%)	[1]	(7.40%)	[1]		(3.90%)	[1]	(4.30%)
Fines and Penalties								6.00%
Other	0.10%	[1]	7.10%	[3]		1.10%	[1]	0.80%
Effective income tax rate	37.30%	[1]	49.40%	[3]		35.40%	[1]	47.10%
Accounting for Uncertainty in Income Taxes [Abstract]
Unrecognized tax benefits that if recognized would affect the effective tax rate	1,363,000,000					1,363,000,000					876,000,000
Information by nature of uncertainty related to unrecognized tax benefits	160,000,000					160,000,000
Increases based on tax positions prior to current year						446,000,000
FIN 48 Tax Remeasurement [Abstract]
FIN 48 Tax Remeasurement Current Tax Expense (Benefit)					70,000,000
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns [Roll Forward]
Increases based on tax positions prior to current year						446,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	288,000,000		85,000,000			436,000,000		373,000,000
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:
State income taxes, net of Federal income tax benefit	5.40%		5.00%			5.20%		5.40%
Qualified nuclear decommissioning trust fund income (losses)	0.00%		0.00%			0.00%		0.00%
Domestic production activities deduction	0.00%		0.00%			0.00%
Tax exempt income	0.00%					0.00%		0.00%
Nontaxable postretirement benefits			0.60%
Health Care Reform Legislation	0.40%					0.90%		0.60%
Amortization of investment tax credit	(0.40%)		(0.50%)			(0.80%)		(0.50%)
Plant basis differences	(0.40%)		(0.50%)			(1.20%)		(0.20%)
Production Tax Credits	0.00%		0.00%			0.00%		0.00%
Other	0.30%		0.00%	[3]		0.80%		0.20%
Effective income tax rate	40.30%		39.60%			39.90%		40.50%
Accounting for Uncertainty in Income Taxes [Abstract]
Unrecognized tax benefits that if recognized would affect the effective tax rate	331,000,000					331,000,000					67,000,000
1999 Sale of Fossil Generating Assets [Abstract]
IRS asserted penalties for understatement of tax						170,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	305,000,000					305,000,000
Status Of Like Kind Exchange Position [Abstract]
Receivable from Exelon intercompany money pool	172,000,000					172,000,000
FIN 48 Tax Remeasurement [Abstract]
FIN 48 Tax Remeasurement Interest Expense					36,000,000
FIN 48 Tax Remeasurement Current Tax Expense (Benefit)					70,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	85,000,000		59,000,000			93,000,000		149,000,000
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:
State income taxes, net of Federal income tax benefit	(0.30%)		3.00%			1.90%		3.20%
Qualified nuclear decommissioning trust fund income (losses)	0.00%		0.00%			0.00%		0.00%
Domestic production activities deduction	0.00%		0.00%			0.00%
Tax exempt income	0.00%		0.00%			0.00%		0.00%
Nontaxable postretirement benefits			0.00%
Health Care Reform Legislation	0.00%					0.00%		0.00%
Amortization of investment tax credit	(0.10%)		(0.30%)			(0.10%)		(0.30%)
Plant basis differences	(6.90%)		(21.00%)			(7.30%)		(9.70%)
Production Tax Credits	0.00%		0.00%			0.00%		0.00%
Other	(0.10%)		0.20%			0.00%		0.00%
Effective income tax rate	27.60%		16.90%			29.50%		28.20%
Accounting for Uncertainty in Income Taxes [Abstract]
Unrecognized tax benefits that if recognized would affect the effective tax rate	44,000,000					44,000,000					44,000,000
Status Of Like Kind Exchange Position [Abstract]
Receivable from Exelon intercompany money pool	1,000,000					1,000,000
FIN 48 Tax Remeasurement [Abstract]
FIN 48 Tax Remeasurement Interest Expense					22,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	35,000,000		25,000,000			122,000,000		118,000,000
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%		0.00%			35.00%		35.00%	[4]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.60%		0.00%			5.60%		2.30%	[4]
Qualified nuclear decommissioning trust fund income (losses)	0.00%		0.00%			0.00%		0.00%	[4]
Domestic production activities deduction	0.00%		0.00%			0.00%
Tax exempt income	0.00%		0.00%			0.00%		0.00%	[4]
Health Care Reform Legislation	0.20%		0.00%			0.20%		(4.60%)	[4]
Amortization of investment tax credit	(0.30%)		0.00%			(0.30%)		2.90%
Plant basis differences	0.10%		0.00%			(0.40%)		7.20%	[4]
Production Tax Credits	0.00%		0.00%			0.00%		0.00%
FIN 48								(14.00%)	[2]
Other	(0.20%)					0.00%		4.50%	[4]
Effective income tax rate	40.40%		0.00%			40.10%		33.30%
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	$ 36,000,000		$ 0			$ 107,000,000		$ (7,000,000)

[1] (a) Exelon activity for the three and nine months ended September 30, 2012 includes the results of Constellation and BGE for March 12, 2012 - September 30, 2012. Generation activity for the three and nine months ended September 30, 2012 includes the results of Constellation for March 12, 2012 - September 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] For the three months ended September 30, 2012, Generation’s effective tax rate was affected by the resolution of uncertain Federal tax positions (5.3%), the finalization of prior year tax return calculations 4.2%, changes in the forecasted activity attributable to noncontrolling interests 4.1%, and other 4.1%.

[4] BGE activity represents the activity for the three and nine months ended September 30, 2012. BGE activity for the three months ended September 30, 2012 resulted in zero pre-tax income and zero income taxes. BGE recognized a loss before income taxes for the nine months ended September 30, 2012. As a result, positive percentages represent an income tax benefit for BGE for the nine months ended September 30, 2012.