Variable Interest Entities (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	$ 550,000,000	[1]	$ 15,000,000
Noncurrent assets	1,802,000,000	[1]	784,000,000
Total Assets	2,352,000,000	[1]	799,000,000
Current liabilities	685,000,000	[1]	181,000,000
Noncurrent liabilities	837,000,000	[1]	77,000,000
Total Liabilities	1,522,000,000	[1]	258,000,000
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	740,000,000	[2]
Total liabilities	333,000,000	[2]
Our ownership interest	97,000,000	[2]
Other ownership interests	310,000,000	[2]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Gross pledged assets	614,000,000		734,000,000
Pledged assets liabilities offset	564,000,000		691,000,000
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	386,000,000	[2]
Total liabilities	219,000,000	[2]
Our ownership interest	0	[2]
Other ownership interests	167,000,000	[2]
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	354,000,000	[2]
Total liabilities	114,000,000	[2]
Our ownership interest	97,000,000	[2]
Other ownership interests	143,000,000	[2]
Letter of Credit [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	5,000,000
Letter of Credit [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	5,000,000
Letter of Credit [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	0
Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	77,000,000
Investments [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	0
Investments [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	77,000,000
Contract Intangible Asset [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	8,000,000
Contract Intangible Asset [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	8,000,000
Contract Intangible Asset [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	0
Payment Guarantee [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	5,000,000
Payment Guarantee [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	0
Payment Guarantee [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Other ownership interests	5,000,000
Net assets pledged for Zion Station decommissioning
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	50,000,000	[3]	43,000,000	[3]
Net assets pledged for Zion Station decommissioning | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	50,000,000	[3]	43,000,000	[3]
Net assets pledged for Zion Station decommissioning | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	0	[3]	0	[3]
Exelon Generation Co L L C [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	519,000,000		15,000,000
Noncurrent assets	1,762,000,000		784,000,000
Total Assets	2,281,000,000		799,000,000
Current liabilities	613,000,000		181,000,000
Noncurrent liabilities	532,000,000		77,000,000
Total Liabilities	1,145,000,000		258,000,000
Projects with significant economic power	9
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Gross pledged assets	614,000,000		734,000,000
Pledged assets liabilities offset	564,000,000		691,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Minority Interest Ownership Percentage By Noncontrolling Owners	1.00%
Exelon Generation Co L L C [Member] | Maximum [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Minority Interest Ownership Percentage By Noncontrolling Owners	6.00%
Exelon Generation Co L L C [Member] | Retail Gas Customer Supply Operation [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Ownership percentage, consolidated variable interest entity (as a percent)	100.00%
Parental guarantee provided	75,000,000
Exelon Generation Co L L C [Member] | Solar Project Limited Liability Companies [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Ownership percentage, consolidated variable interest entity (as a percent)	100.00%
Business Acquisitions, Megawatts Acquired	230
Aggregate amount of debt with third parties	220,000,000
Exelon Generation Co L L C [Member] | Wind Project Limited Liability Companies [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Ownership percentage, consolidated variable interest entity (as a percent)	100.00%
Projects with significant economic power	10
Exelon Generation Co L L C [Member] | Wind Project Limited Liability Companies [Member] | Minimum [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Minority Interest Ownership Percentage By Noncontrolling Owners	99.00%
Exelon Generation Co L L C [Member] | Wind Project Limited Liability Companies [Member] | Maximum [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Minority Interest Ownership Percentage By Noncontrolling Owners	94.00%
PECO Energy Co [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Amount of PECO's stranded costs authorized to be recovered by the PAPUC	5,000,000,000
Baltimore Gas and Electric Company [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	30,000,000	[4]	30,000,000	[4]
Noncurrent assets	0	[4]	0	[4]
Total Assets	30,000,000	[4]	30,000,000	[4]
Current liabilities	71,000,000	[4]	69,000,000	[4]
Noncurrent liabilities	265,000,000	[4]	332,000,000	[4]
Total Liabilities	336,000,000	[4]	401,000,000	[4]
Remittance of payments received from customers for rate stabilization to BondCo.	$ 85,000,000		$ 92,000,000		$ 90,000,000

[1] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[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 Generation’s and Exelon’s balance sheet related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $614 million and $734 million as of December 31, 2012 and December 31, 2011, respectively; offset by payables to ZionSolutions LLC of $564 million and $691 million as of December 31, 2012 and December 31, 2011, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE. See Note 13 – Asset Retirement Obligations for further discussion.

[4] Amounts related to BGE are presented for the standalone entity as of both December 31, 2012 and 2011.