Guarantees (Details) (USD $)	Sep. 30, 2011
Guarantee Obligations
Stated limit of outstanding guarantee	$ 9,400,000,000
Constellation Energy;
Guarantee Obligations
Stated limit of outstanding guarantee	9,100,000,000
Baltimore Gas and Electric Company
Guarantee Obligations
Stated limit of outstanding guarantee	300,000,000
Parent guarantor of Generation and New Energy businesses
Guarantee Obligations
Stated limit of outstanding guarantee	8,600,000,000
Estimated exposure under commercial transactions	1,000,000,000
Parent guarantor of CENG business
Guarantee Obligations
Stated limit of outstanding guarantee	500,000,000
Estimated fair value exposure under commercial transactions recorded on our consolidated balance sheets	11,100,000
BGE guarantor of Trust Preferred Securities
Guarantee Obligations
Stated limit of outstanding guarantee	$ 250,000,000