Capitalization (Details 4) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended						12 Months Ended	1 Months Ended				1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Baltimore Gas and Electric Company Y	Dec. 31, 2010 Baltimore Gas and Electric Company	Jul. 01, 2000 Baltimore Gas and Electric Company	Dec. 31, 2011 Baltimore Gas and Electric Company Medium-term notes, Series E	Jun. 30, 2007 Bond Co	Dec. 31, 2011 Bond Co 5.47% Rate Stabilization Bonds maturing in October 2012	Dec. 31, 2011 Bond Co 5.72% Rate Stabilization Bonds maturing in April 2016	Dec. 31, 2011 Bond Co 5.82% Rate Stabilization Bonds maturing in April 2017	Nov. 30, 2003 BGE Capital Trust II	Nov. 21, 2003 BGE Capital Trust II
Capitalization disclosures
Total Long-term Debt Issued	$ 564.2	$ 550.0	$ 136.1	$ 300.0				$ 623.2
Term of BGE's residential electric customers to pay a usage-based, non-bypassable charge securing the rate stabilization bonds (in years)				10
Interest rate (as a percent)									5.47%	5.72%	5.82%
Rate stabilization bonds				394.6	454.4				55.4	220.0	119.2
BGE's transfer of tax-exempt debt to Generation business						278.0
Preferred stock, issued (in shares)													10,000,000
6.20% deferrable interest subordinated debentures due October 15, 2043 to wholly owned BGE Capital Trust II relating to trust preferred securities	257.7	257.7		257.7	257.7
Preferred stock distribution rate (as a percent)												6.20%
BGE's contingent liability for tax-exempt debt transferred to Generation business				20.0
Weighted average interest rate							6.75%
Issuance of trust preferred securities in 2003												$ 250
Liquidation amount per preferred security in addition to accrued but unpaid distributions (in dollars per share)													$ 25