Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended																																							3 Months Ended		9 Months Ended
	Sep. 30, 2013 VIE		Dec. 31, 2012 VIE		Sep. 30, 2013 Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Commercial Agreement Variable Interest Entities [Member]		Sep. 30, 2013 Equity Method Investment Variable Interest Entities [Member]		Dec. 31, 2012 Equity Method Investment Variable Interest Entities [Member]		Dec. 31, 2012 Letter of Credit [Member] Maximum [Member]	Dec. 31, 2012 Letter of Credit [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Sep. 30, 2013 Investments [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member]	Sep. 30, 2013 Investments [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Sep. 30, 2013 Contract Intangible Asset [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member]	Sep. 30, 2013 Contract Intangible Asset [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Sep. 30, 2013 Payment Guarantee [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member]	Sep. 30, 2013 Payment Guarantee [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Sep. 30, 2013 Net assets pledged for Zion Station decommissioning		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member]		Sep. 30, 2013 Net assets pledged for Zion Station decommissioning Maximum [Member] Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member] Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Power Contract Monetization Entities [Member]	Sep. 30, 2013 Variable Interes tEntity Primary Beneficiary [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	$ 391		$ 550	[1]																																	$ 330	$ 519	[1]	$ 50	$ 30
Noncurrent assets	1,900		1,802	[1]																																	1,877	1,762	[1]			3		3
Total Assets	2,291		2,352	[1]																																	2,207	2,281	[1]	53	30
Current liabilities	453		685	[1]																																	366	613	[1]	77	71
Noncurrent liabilities	859		837	[1]																																	608	532	[1]	230	265
Total Liabilities	1,312		1,522	[1]																																	974	1,145	[1]	307	336
Deferred tax assets			116
Deferred tax liabilities			62																																	53
Remittance of payments received from customers for rate stabilization to BondCo.																																										24	27	63	62
Parental guarantee provided																																								75	75
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of Variable Interest Entities not consolidated by equity holders	7		9
Number Of Variable Interest Entities Consolidated	4		5
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	481	[2]	740	[2]	115	[2]	386	[2]	366	[2]	354	[2]																							146
Total liabilities	129	[2]	333	[2]	3	[2]	219	[2]	126	[2]	114	[2]																							42
Our ownership interest	97	[2]	97	[2]					97	[2]	97	[2]
Other ownership interests	255	[2]	310	[2]	112	[2]	167	[2]	143	[2]	143	[2]
Our maximum exposure to loss													5	5	78	77	78	77	9	8	9	8	5	5	5	5	43	[3]	50	[3]	43	[3]	50	[3]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Gross pledged assets	486		614																																		486	614
Pledged assets liabilities offset	$ 443		$ 564																																		$ 443	$ 564

[1] Includes total assets of $146 million and total liabilities of $42 million as of December 31, 2012 related to a retail power supply company that is no longer a consolidated VIE as of September 30, 2013.

[2] These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

[3] These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $486 million and $614 million as of September 30, 2013 and December 31, 2012, respectively; offset by payables to ZionSolutions LLC of $443 million and $564 million as of September 30, 2013 and December 31, 2012, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.