Related Party Transactions (Details) (USD $)	9 Months Ended	12 Months Ended				1 Months Ended		12 Months Ended		1 Months Ended		2 Months Ended	12 Months Ended				2 Months Ended	12 Months Ended		2 Months Ended	12 Months Ended					1 Months Ended				12 Months Ended
	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010 Y	Dec. 31, 2009	Dec. 31, 2011 Power services agency agreement (PSA) Exelon Corporation	Jun. 30, 2011 CENG	May 31, 2011 CENG	Dec. 31, 2011 CENG	Dec. 31, 2009 CENG Y	May 31, 2011 CENG Revolving promissory note	Dec. 31, 2011 CENG Revolving promissory note	Dec. 31, 2009 CENG Power purchase agreement (PPA)	Dec. 31, 2011 CENG Power purchase agreement (PPA)	Dec. 31, 2010 CENG Power purchase agreement (PPA)	Dec. 31, 2011 CENG Power purchase agreement (PPA) Minimum	Dec. 31, 2011 CENG Power purchase agreement (PPA) Maximum	Dec. 31, 2009 CENG Power services agency agreement (PSA)	Dec. 31, 2011 CENG Power services agency agreement (PSA) Y	Dec. 31, 2010 CENG Power services agency agreement (PSA)	Dec. 31, 2009 CENG Administrative services agreement (ASA)	Dec. 31, 2011 CENG Administrative services agreement (ASA)	Dec. 31, 2010 CENG Administrative services agreement (ASA)	Dec. 31, 2011 Baltimore Gas and Electric Company	Dec. 31, 2010 Baltimore Gas and Electric Company	Dec. 31, 2009 Baltimore Gas and Electric Company	May 31, 2011 EDF Revolving promissory note	May 31, 2011 Constellation Energy. Revolving promissory note	Aug. 31, 2011 CEP	May 31, 2011 CEP	Dec. 31, 2011 CEP
Related Party Transactions:
Required purchases of power from CENG's nuclear plants not sold to third parties (as a percent)															85.00%	90.00%
Purchase of nuclear output of CENG (as a percent)								50.01%
Purchase of nuclear output by EDF (as a percent)								49.99%
Term of agreement with CENG (in years)			5						5									5
Average expected annual revenue from agreement with CENG																		$ 16,000,000
Expected 2011 revenue from agreement with CENG																					48,000,000
Increase (Decrease) in Earnings												(122,500,000)	(888,400,000)	(900,800,000)			2,700,000	16,100,000	16,100,000	10,000,000	48,000,000	66,000,000
Income Statement Classification													Fuel and purchased energy expenses					Nonregulated revenues			Operating expenses
Amount receivable from (payable to) related to agreements with CENG													(47,500,000)								4,000,000
Maximum cost of service per month upon closing of merger with Exelon					358,000
Maximum borrowing capacity		130,000,000
Percentage of request for borrowings submitted to entity (as a percent)																											50.00%
Percentage of request for borrowings submitted to entity's subsidiaries (as a percent)																										50.00%
Variable rate offered by prime banks										rate at which deposits of United States dollars are offered by prime banks in the London interbank market
Spread on variable rate offered by prime banks (as a percent)										2.50%
Outstanding borrowings											30,000,000
Pre-tax gain on U. S. Department of Energy settlement	35,500,000	58,400,000				93,800,000
Net (loss) gain on divestitures, pre-tax		57,300,000	245,800,000	(468,800,000)																								23,000,000	11,400,000	10,700,000
Proceeds from U.S. Department of Energy settlement								93,800,000
Electricity purchased for resale expenses																							348,200,000	428,000,000	623,500,000
Corporate function costs directly assigned or allocated to BGE																							178,600,000	184,800,000	164,700,000
CENG issued an unsecured revolving promissory note to borrow up to an aggregate principal amount							$ 62,500,000