Pending Merger with Exelon Corporation (Details) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	Apr. 30, 2011	Jun. 30, 2011	Jun. 30, 2011	Apr. 28, 2011
Combined entity
Pending merger with Exelon Corporation
Proposed amount of rebate for residential customers (per customer)				$ 100
Commitments made by combined entity				250,000,000
Constellation Energy.
Pending merger with Exelon Corporation
Number of common shares of Constellation Energy to be cancelled and converted into the right to receive for each share of Exelon (in shares)	0.93
Termination fee payable under specified circumstances				200,000,000
Pre-tax costs related to our pending merger		31,800,000	31,800,000
Exelon Corporation
Pending merger with Exelon Corporation
Termination fee payable under specified circumstances				$ 800,000,000