Income Taxes (Details) (USD $)	3 Months Ended				12 Months Ended				3 Months Ended	12 Months Ended	3 Months Ended					12 Months Ended		3 Months Ended						3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2013	Dec. 31, 1999	Mar. 31, 2011 Deferred Tax Impact [Member]	Dec. 31, 2011 Deferred Tax Impact [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member] Deferred Tax Impact [Member]	Mar. 31, 2014 Commonwealth Edison Co [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member]		Mar. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2013 Commonwealth Edison Co [Member]	Mar. 31, 2014 PECO Energy Co [Member]	Mar. 31, 2013 PECO Energy Co [Member]	Mar. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2013 PECO Energy Co [Member]	Mar. 31, 2014 Baltimore Gas and Electric Company [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation
U.S. Federal statutory rate	35.00%	35.00%									35.00%	35.00%							35.00%	35.00%				35.00%	35.00%			35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	(57.60%)	68.00%									9.70%	82.00%							5.50%	5.80%				1.20%	2.80%			5.20%	5.70%
Qualified nuclear decommissioning trust fund income (losses)	44.20%	62.00%									(4.60%)	(192.30%)
Domestic production activities deduction	(27.80%)	(2.40%)									2.90%	7.40%
Tax exempt income		(1.60%)										4.80%
Health Care Reform Legislation	1.30%	2.20%																	0.10%	(0.50%)								0.20%	0.40%
Amortization of investment tax credit	(18.00%)	(25.80%)									1.70%	75.60%							(0.30%)	0.40%				(0.10%)	(0.10%)			(0.20%)	(0.20%)
Plant basis differences	(31.40%)	(24.90%)																	(0.60%)	0.90%				(8.70%)	(6.70%)			(0.60%)	(0.60%)
Production Tax Credits	(36.50%)	(21.70%)									3.80%	67.20%
Other	(47.70%)	7.40%									3.30%	(74.10%)	[1]						0.20%	0.10%	[1]			0.20%	0.10%			0.10%	0.40%
Effective income tax rate	(138.50%)	98.20%									51.80%	5.60%	[1]						39.90%	41.70%				27.60%	31.10%			39.70%	40.70%
Accounting for Uncertainty in Income Taxes [Abstract]
Unrecognized tax benefits that if recognized would affect the effective tax rate	$ 1,860,000,000						$ 2,175,000,000				$ 1,394,000,000						$ 1,415,000,000		$ 155,000,000				$ 324,000,000	$ 44,000,000			$ 44,000,000
Information by nature of uncertainty related to unrecognized tax benefits											225,000,000
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											155,000,000
IRS asserted penalties for understatement of tax	265,000,000																		170,000,000
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position	840,000,000																		300,000,000
IRS asserted penalties for understatement of tax related to like-kind exchange	87,000,000
Status Of Like Kind Exchange Position [Abstract]
Receivable from Exelon intercompany money pool											0						44,000,000		172,000,000					0			0
FIN 48 Tax Remeasurement [Abstract]
FIN 48 Tax Remeasurement Interest Expense				65,000,000																		36,000,000				22,000,000
FIN 48 Tax Remeasurement Current Tax Expense (Benefit)															70,000,000							70,000,000
Tax Settlement [Abstract]
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]
Gross Deferred Income tax benefit recorded as a result of re-apportionment of state income taxes			116,000,000		3,000,000					8,000,000				14,000,000
Gross Deferred Income tax expense recorded as a result of re-apportionment of state income taxes									22,000,000	1,000,000						7,000,000		11,000,000
Deferred state tax liability resulting from purchase accounting			44,000,000											14,000,000
DeferredStateTaxAssetFromStateTaxApportionment			72,000,000
TaxesPayableCurrent
Taxes Payable Current	285,000,000
Income Tax Expense Benefit Continuing Operations [Line Items]
Income Tax Expense (Benefit)	$ (54,000,000)	$ 56,000,000									$ (199,000,000)	$ (1,000,000)							$ 65,000,000	$ (58,000,000)				$ 34,000,000	$ 55,000,000			$ 58,000,000	$ 55,000,000

[1]  Generation recognized a loss before income taxes for the three months ended March 31, 2014. As a result, positive percentages represent an income tax benefit for Generation for the three months ended March 31, 2014