Supplemental Financial Information - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives	[1]	$ (26)
Amount included in capital expenditures			$ 74
Smart Grid Grant Reimbursements			95
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amount included in capital expenditures		2	27
Smart Grid Grant Reimbursements		5	37
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amount included in capital expenditures			47
Smart Grid Grant Reimbursements			$ 58
Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives		$ 26

[1] In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.