Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended																																							3 Months Ended		6 Months Ended
	Jun. 30, 2013 VIE		Dec. 31, 2012		Jun. 30, 2013 Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Commercial Agreement Variable Interest Entities [Member]		Jun. 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]	Jun. 30, 2013 Investments [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member]	Jun. 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]	Jun. 30, 2013 Contract Intangible Asset [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member]	Jun. 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]	Jun. 30, 2013 Payment Guarantee [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member]	Jun. 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]	Jun. 30, 2013 Net assets pledged for Zion Station decommissioning		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member]		Jun. 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]		Jun. 30, 2013 Variable Interes tEntity Primary Beneficiary [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Jun. 30, 2012 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	$ 462		$ 550																																	$ 426	$ 519	$ 27	$ 30
Noncurrent assets	1,961		1,802																																	1,938	1,762
Total Assets	2,423		2,352																																	2,364	2,281	27	30
Current liabilities	474		685																																	391	613	73	71
Noncurrent liabilities	981		837																																	728	532	230	265
Total Liabilities	1,455		1,522																																	1,119	1,145	303	336
Deferred tax assets			116																																115
Deferred tax liabilities			62																																57
Remittance of payments received from customers for rate stabilization to BondCo.																																								17	15	39	35
Parental guarantee provided																																						75	75
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of Variable Interest Entities not consolidated by equity holders	8
Number Of Variable Interest Entities Consolidated	5
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	550	[1]	740	[1]	202	[1]	386	[1]	348	[1]	354	[1]
Total liabilities	191	[1]	333	[1]	83	[1]	219	[1]	108	[1]	114	[1]
Our ownership interest	97	[1]	97	[1]					97	[1]	97	[1]
Other ownership interests	262	[1]	310	[1]	119	[1]	167	[1]	143	[1]	143	[1]
Our maximum exposure to loss													5	5	78	77	78	77	8	8	8	8	5	5	5	5	47	[2]	50	[2]	47	[2]	50	[2]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Gross pledged assets	538		614																																	538	614
Pledged assets liabilities offset	$ 491		$ 564																																	$ 491	$ 564

[1] 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.

[2] These items represent amounts on Generation’s and Exelon’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 $538 million and $614 million as of June 30, 2013 and December 31, 2012, respectively; offset by payables to ZionSolutions LLC of $491 million and $564 million as of June 30, 2013 and December 31, 2012, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.