Income Taxes (Details) (USD $)	3 Months Ended				6 Months Ended			12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Mar. 31, 2011	Jun. 30, 2013		Jun. 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	4.10%	[1]	3.50%		8.60%	[1]	(10.70%)
Qualified nuclear decommissioning trust fund income (losses)	(1.80%)	[1]	(2.00%)		2.80%	[1]	6.30%
Domestic production activities deduction	0.10%	[1]	0.70%		0.00%	[1]	(0.20%)
Tax exempt income	(0.10%)	[1]	(0.40%)		(0.20%)	[1]	(0.40%)
Nontaxable postretirement benefits			0.30%
Health Care Reform Legislation	0.10%	[1]			0.20%	[1]	0.20%
Amortization of investment tax credit	(1.80%)	[1]	(0.70%)		(3.50%)	[1]	(0.70%)
Plant basis differences	(1.40%)	[1]	(0.70%)		(3.10%)	[1]	(0.60%)
Production Tax Credits	(1.40%)	[1]	(2.20%)		(2.80%)	[1]	(2.60%)
Fines and Penalties							6.10%
Merger Expenses			(0.80%)				5.60%
Other	(0.30%)	[1]			0.10%	[1]	(1.30%)
Effective income tax rate	32.50%	[1]	30.40%		37.10%	[1]	36.70%
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					86,000,000
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)	239,000,000		126,000,000		294,000,000		284,000,000
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	3.50%	[1]	2.30%		0.40%	[1]	1.60%
Qualified nuclear decommissioning trust fund income (losses)	(2.70%)	[1]	(3.80%)		4.80%	[1]	8.00%
Domestic production activities deduction	0.20%	[1]	1.60%		(0.10%)	[1]	(0.20%)
Tax exempt income	(0.20%)	[1]	(0.80%)		(0.40%)	[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	(2.50%)	[1]	(0.70%)		(5.60%)	[1]	(0.60%)
Plant basis differences	0.00%	[1]	0.00%		0.00%	[1]	0.00%
Production Tax Credits	(2.20%)	[1]	(4.00%)		(4.90%)	[1]	(3.40%)
Fines and Penalties							7.60%
Other	0.10%	[1]	(3.60%)		3.10%	[1]	(1.00%)
Effective income tax rate	31.20%	[1]	26.00%		32.30%	[1]	46.50%
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	35,000,000				35,000,000
Increases based on tax positions prior to current year					446,000,000
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible Amount Of Unrecorded Benefit	35,000,000				35,000,000
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)	149,000,000		58,000,000		148,000,000		289,000,000
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	5.60%		5.20%		4.10%		5.70%
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%		0.00%
Tax exempt income	0.00%		0.00%		0.00%		0.00%
Nontaxable postretirement benefits			1.00%
Health Care Reform Legislation	0.40%				5.70%		0.60%
Amortization of investment tax credit	(0.30%)		(0.80%)		(4.90%)		(0.50%)
Plant basis differences	(0.40%)		0.10%		(8.70%)		0.00%
Production Tax Credits	0.00%		0.00%		(0.30%)		0.00%
Other	0.40%		0.30%		5.50%		0.30%
Effective income tax rate	40.70%		40.80%		36.40%		41.10%
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	306,000,000				306,000,000
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)	66,000,000		29,000,000		8,000,000		90,000,000
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	2.90%		3.10%		2.90%		3.30%
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%		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	(8.60%)		(3.60%)		(7.50%)		(3.60%)
Production Tax Credits	0.00%		0.00%		0.00%		0.00%
Other	(0.10%)		0.20%		0.00%		0.00%
Effective income tax rate	29.10%		34.40%		30.30%		34.40%
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	263,000,000				263,000,000				0
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)	32,000,000		42,000,000		87,000,000		93,000,000
Baltimore Gas and Electric Company [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	5.60%		6.20%		5.70%		2.30%
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%		0.00%
Tax exempt income	0.00%		0.00%		0.00%		0.00%
Health Care Reform Legislation	(0.30%)		2.70%		0.20%		(3.10%)
Amortization of investment tax credit	(0.60%)		(1.70%)		(0.30%)		3.80%
Plant basis differences	(0.70%)		(4.70%)		(0.60%)		10.60%
Production Tax Credits	0.00%		0.00%		0.00%		0.00%
FIN 48							(18.30%)
Other	0.00%		(1.50%)		(0.20%)		3.00%
Effective income tax rate	39.00%		36.00%		39.80%		33.30%
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	16,000,000		9,000,000		70,000,000		(7,000,000)
Exelon Corporate [Member]
Increase (decrease) due to:
Other			(2.30%)
Accounting for Uncertainty in Income Taxes [Abstract]
Information by nature of uncertainty related to unrecognized tax benefits	35,000,000				35,000,000
Increases based on tax positions prior to current year					446,000,000
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible Amount Of Unrecorded Benefit	35,000,000				35,000,000
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

[1] (a) 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.