Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	May 31, 2010	Dec. 31, 2011 treatment Y method Entity segment counties counterparty	Dec. 31, 2010	Dec. 31, 2009	Nov. 06, 2011	Dec. 31, 2011 Maximum	Dec. 31, 2010 Maximum	Nov. 30, 2010 Maximum	Dec. 31, 2011 Minimum	Dec. 31, 2010 Minimum	Nov. 30, 2010 Minimum
Significant Accounting Policies
Electric Domestic Regulated Revenue		$ 2,320.7	$ 2,752.1	$ 2,820.7
Gas Domestic Regulated Revenue		664.5	704.9	753.8
Equity in earnings of investments accounted for under the equity method of accounting
Number of business segments		3
Number of counties		10
Number of accounting methods		3
Number of types of entities consolidated		2
Number of accounting treatments to recognize and report revenues in operations		2
Number of consolidated variable interest entities		4
Equity method investments ownership (as a percent)				50.01%		50.01%	50.01%		20.00%	20.00%
Threshold percentage of voting interest held for investments recorded with the cost method of accounting (as a percent)		20.00%
Percent of membership interest in CENG sold				49.99%	49.99%
Term of suspension of collecting shareholder return component of the administrative fee for residential SOS service by BGE (in years)		10
Increase in annual distribution rates BGE is authorized to make	31.0
Rate of return for increase in distribution rates BGE is authorized to make (as a percent)	8.06%
Return on equity for increase in distribution rates BGE is authorized to make (as a percent)	9.86%
Equity ratio for increase in distribution rates BGE is authorized to make (as a percent)	52.00%
Percentage of fixed-price contracts for forecasted system supply requirements for the November through March period required by the public service commission to be procured by BGE (as a percent)								20.00%			10.00%
Increase in annual gas distribution rates BGE is authorized to make	$ 9.8
Rate of return for increase in gas distribution rates BGE is authorized to make (as a percent)	7.90%
Return on equity for increase in gas distribution rates BGE is authorized to make (as a percent)	9.56%
Equity ratio for increase in gas distribution rates BGE is authorized to make (as a percent)	52.00%
Concentration of credit risk trigger for disclosure, percentage (as a percent)		10.00%
Concentration of credit risk, percentage (as a percent)		29.00%
Counterparties exceeding the maximum credit exposure trigger percentage, number		2
Percent of credit risk exposure in large power cooperatives		29.00%