Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Financial Data:
Revenues									$ 13,758.2	$ 14,340.0	$ 15,598.8
(Loss) Income from Operations									(197.0)	(1,243.0)	7,981.0
Net Income (Loss)									(306.8)	(931.8)	4,503.4
Net Income (Loss) Attributable to Common Stock									(340.3)	(982.6)	4,443.4
Earnings (Loss) Per Share of Common Stock-Diluted (in dollars per share)									$ (1.70)	$ (4.90)	$ 22.19
Baltimore Gas and Electric Company
Quarterly Financial Data:
Revenues	656.5	722.9	656.2	957.5	784.8	856.1	751.5	1,069.3	2,993.1	3,461.7	3,579.0
(Loss) Income from Operations	85.9	22.8	52.7	153.4	85.8	75.6	55.9	136.9	314.8	354.2	268.4
Net Income (Loss)	36.4	1.6	16.6	81.1	34.4	31.8	17.0	64.4	135.7	147.6
Net Income (Loss) Attributable to Common Stock	33.1	(1.7)	13.3	77.8	31.1	28.5	13.7	61.1	122.5	134.4	84.8
Constellation Energy;
Quarterly Financial Data:
Revenues	2,952.8	3,875.4	3,359.8	3,570.2	3,474.6	3,968.9	3,309.9	3,586.6	13,758.2	14,340.0
Fuel and Purchased Energy Expenses (includes amounts from affiliates)	2,246.5	2,984.6	2,380.9	2,673.0					10,285.0
(Loss) Income from Operations	(904.5)	229.8	260.1	217.6	406.7	(2,246.7)	181.9	415.1	(197.0)	(1,243.0)
Net Income (Loss)	(592.2)	97.9	108.1	79.4	168.1	(1,375.0)	83.8	191.3	(306.8)	(931.8)
Net Income (Loss) Attributable to Common Stock	$ (583.6)	$ 73.7	$ 99.2	$ 70.4	$ 159.8	$ (1,406.5)	$ 72.6	$ 191.5	$ (340.3)	$ (982.6)
Earnings (Loss) Per Share from Operations-Diluted (in dollars per shares)	$ (2.91)	$ 0.36	$ 0.49	$ 0.35	$ 0.79	$ (6.99)	$ 0.36	$ 0.95	$ (1.70)	$ (4.90)
Earnings (Loss) Per Share of Common Stock-Diluted (in dollars per share)	$ (2.91)	$ 0.36	$ 0.49	$ 0.35	$ 0.79	$ (6.99)	$ 0.36	$ 0.95	$ (1.70)	$ (4.90)