Supplemental Financial Information - Narrative (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Supplemental Financial Information Tables [Line Items]
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