Changes in Accumulated Other Comprehensive Income (Reclassification out of Accumulated Other Comprehensive Income)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	$ 6,141		$ 5,966	$ 12,223		$ 10,656
Interest Expense	246		250	863		439
Other income and deductions	(269)		(299)	(721)		(299)
Income before income taxes	736		415	792		774
Income taxes	239		126	294		284
Net income (loss)	497		289	498		490
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	(21)		(57)	(30)		(79)
Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	35	[1]		41	[1]
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	141	[1]		239	[1]
Income taxes	(52)	[1]		(92)	[1]
Net income (loss)	89	[1]		147	[1]
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	141	[1]		240	[1]
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	0	[1]		(1)	[1]
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	(83)	[1],[2]		(166)	[1],[2]
Income taxes	32	[1]		65	[1]
Net income (loss)	(51)	[1],[2]		(101)	[1]
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]
Prior service costs	(1)	[1],[2]		(1)	[1],[2]
Actuarial gains/losses	(82)	[1],[2]		(165)	[1],[2]
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	(5)	[1]		(8)	[1]
Income taxes	2	[1]		3	[1]
Net income (loss)	(3)	[1]		(5)	[1]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	(5)	[1]		(8)	[1]
Exelon Generation Co L L C [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	4,070		3,765	7,603		6,508
Interest Expense	93		85	176		138
Other income and deductions	(126)		(161)	(81)		(35)
Income before income taxes	477		223	458		621
Income taxes	149		58	148		289
Net income (loss)	328		165	310		332
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	(21)		(57)	(30)		(79)
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)	141	[1]		274	[1]
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]
Income before income taxes	237	[1]		460	[1]
Income taxes	(93)	[1]		(181)	[1]
Net income (loss)	144	[1]		279	[1]
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	236	[1]		459	[1]
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	[1]		1	[1]
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	(5)	[1]		(8)	[1]
Income taxes	2	[1]		3	[1]
Net income (loss)	(3)	[1]		(5)	[1]
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Pension And Other Postretirement Benefit PlansTax [Abstract]
Gain (loss) on equity method investments	(5)	[1]		(8)	[1]
Commonwealth Edison Co [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	1,080		1,281	2,239		2,670
Interest Expense	72		71	422		150
Other income and deductions	(70)		(71)	(418)		(149)
Income before income taxes	162		71	22		219
Income taxes	66		29	8		90
Net income (loss)	96		42	14		129
PECO Energy Co [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	672		715	1,567		1,590
Interest Expense	25		28	51		56
Other income and deductions	(28)		(29)	(54)		(57)
Income before income taxes	110		122	287		270
Income taxes	32		42	87		93
Net income (loss)	78		80	200		177
Baltimore Gas and Electric Company [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operating revenues	653		616	1,533		1,312
Interest Expense	32		34	66		75
Other income and deductions	(28)		(27)	(57)		(62)
Income before income taxes	41		25	176		(21)
Income taxes	16		9	70		(7)
Net income (loss)	$ 25		$ 16	$ 106		$ (14)

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

[2] (b) This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see note 14 for additional details).