Changes in Accumulated Other Comprehensive Income (Changes in accumulated other comprehensive income by component)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended														3 Months Ended			9 Months Ended															9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013 Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Sep. 30, 2013 Accumulated Net Unrealized Investment Gain Loss [Member]		Sep. 30, 2013 Accumulated Defined Benefit Plans Adjustment [Member]		Sep. 30, 2013 Accumulated Translation Adjustment [Member]		Sep. 30, 2013 Accumulated Equity Investment [Member]		Sep. 30, 2013 Accumulated Other Comprehensive (Loss) Income, Net	Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Translation Adjustment [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Equity Investment [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Other Comprehensive (Loss) Income, Net	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]		Dec. 31, 2012 PECO Energy Co [Member]		Sep. 30, 2013 PECO Energy Co [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Dec. 31, 2012 PECO Energy Co [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance				$ (2,767)	[1]		$ 368	[1]			$ (3,137)	[1]	$ 0	[1]	$ 2	[1]					$ 513	[1]		$ 512	[1]					$ 1	[1]			$ 0	$ 0		$ 1	[1]	$ 1	[1]	$ 1	[1]	$ 1	[1]	$ 0	[1]	$ 0	[1]
OCI before reclassifications				138	[1]		25	[1]	(1)	[1]	73	[1]	(5)	[1]	46	[1]					53	[1]		12	[1]	(1)	[1]	(5)	[1]	47	[1]
Amounts reclassified from AOCI				(32)	[1],[2],[3]		(194)	[1],[2],[3]			157	[1],[2],[3]			5	[1],[2],[3]					(323)	[1],[2],[3]		(328)	[1],[2],[3]					5	[1],[2],[3]
Net current-period OCI	12		(92)	106	[1]	45	(169)	[1]			230	[1]	(5)	[1]	51	[1]		(32)		(152)	(270)	[1]	(163)	(316)	[1]	(1)	[1]	(5)	[1]	52	[1]	(270)	1			1
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(2,661)	[1]		(2,661)	[1]		199	[1]			(2,907)	[1]	(5)	[1]	53	[1]		243	[1]		243	[1]		196	[1]	(1)	[1]	(5)	[1]	53	[1]			0	0		1	[1]	1	[1]	1	[1]	1	[1]	0	[1]	0	[1]
OtherComprehensiveIncomeLossTaxParentheticalDisclosuresAbstract
Prior service costs			1			2
Actuarial loss reclassified to periodic cost, taxes	(33)		(28)	(97)		(82)
Transition obligation			1			2
Pension and non-pension postretirement benefit plan valuation adjustment, taxes	6		43	(44)		51
Change in unrealized gain (loss) on cash flow hedges, taxes	(35)		(57)	(109)		36												(36)		(113)	(209)		(122)
Change in unrealized gain (loss) on marketable securities, taxes						1
Change in unrealized gain (loss) on equity investments taxes	9		11	32		15												9		11	32		15
Deferred Compensation Unit Valuation Adjustment tax				6
Other comprehensive income, income taxes	$ 1		$ (59)	$ 70		$ 87											$ 70	$ (27)		$ (102)	$ (177)		$ (107)									$ 177

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

[2] (b) See next table for details about these reclassifications.

[3] (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).