Changes in Accumulated Other Comprehensive Income (Reclassification out of Accumulated Other Comprehensive Income)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	$ 6,502	[1]	$ 6,579	[1]	$ 18,725	[2]	$ 17,235	[2]
Interest Expense	228		240		1,091		678
Other income and deductions	(79)		(145)		(799)		(444)
Income before income taxes	1,175		458		1,968		1,232
Income taxes	439		161		733		445
Net income (loss)	736		297		1,235		787
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Prior service costs			1				2
Transition obligation			1				2
Gain (loss) on equity method investments	37		10		7		(69)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(8)	[3]			32	[3]
Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	83	[3]			322	[3]
Income taxes	(35)	[3]			(128)	[3]
Net income (loss)	48	[3]			194	[3]
Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	84	[3]			324	[3]
Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	(1)	[3]			(2)	[3]
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(93)	[3]			(259)	[3]
Income taxes	37	[3]			102	[3]
Net income (loss)	(56)	[3]			(157)	[3]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Deferred compensation unit	(1)	[3],[4]			(1)	[3],[4]
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Plans Defined Benefit [Member]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Actuarial gains/losses	(92)	[3]			(257)	[3]
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Equity Investment Reclassified Out of Accumulated Other Comprehensive Income [Member]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Prior service costs					(1)	[3]
Equity Method Investments | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	0				(8)	[3]
Income taxes	0				3	[3]
Net income (loss)	0				(5)	[3]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	0				(8)	[3]
Exelon Generation Co L L C [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	4,255		4,031		11,858		10,539
Interest Expense	82		85		257		223
Other income and deductions	52		(2)		(28)		(38)
Income before income taxes	773		172		1,231		792
Income taxes	288		85		436		373
Net income (loss)	485		87		795		419
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	37		10		7		(69)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	50	[3]			323	[3]
Exelon Generation Co L L C [Member] | Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest Expense					0	[3]
Income before income taxes	83	[3]			543	[3]
Income taxes	(33)	[3]			(215)	[3]
Net income (loss)	50	[3]			328	[3]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments					(8)	[3]
Exelon Generation Co L L C [Member] | Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	84	[3]			543	[3]
Exelon Generation Co L L C [Member] | Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	(1)	[3]
Exelon Generation Co L L C [Member] | Equity Method Investments | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	0				(8)	[3]
Income taxes	0				3	[3]
Net income (loss)	0				(5)	[3]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	0
Commonwealth Edison Co [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	1,156		1,484		3,395		4,154
Interest Expense	71		71		493		221
Other income and deductions	(67)		(69)		(485)		(218)
Income before income taxes	211		149		233		368
Income taxes	85		59		93		149
Net income (loss)	126		90		140		219
PECO Energy Co [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	728		806		2,295		2,396
Interest Expense	26		29		77		85
Other income and deductions	(28)		(30)		(82)		(88)
Income before income taxes	127		148		414		418
Income taxes	35		25		122		118
Net income (loss)	92		123		292		300
Baltimore Gas and Electric Company [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	737		720		2,271		2,032
Interest Expense	29		35		94		110
Other income and deductions	(25)		(30)		(81)		(92)
Income before income taxes	89		0		267		(21)
Income taxes	36		0		107		(7)
Net income (loss)	$ 53		$ 0		$ 160		$ (14)

[1] For the three months ended September 30, 2013 and 2012, utility taxes of $21 million and $28 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2013 and 2012, utility taxes of $65 million and $67 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2013 and 2012, utility taxes of $33 million and $40 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2013 and 2012, utility taxes of $20 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2013 and 2012, utility taxes of $60 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2013 and 2012, utility taxes of $182 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2013 and 2012, utility taxes of $97 million and $108 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2013 and period of March 12, 2012 through September 30, 2012, utility taxes of $62 million and $42 million, respectively, are included in revenues and expenses for BGE.

[3] (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in net income.

[4] (c) Amortization of deferred compensation unit is allocated to capital and operating and maintenance expense.