Regulatory Matters - Narrative (Details) (USD $)	0 Months Ended	9 Months Ended	12 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended					3 Months Ended		3 Months Ended	48 Months Ended	0 Months Ended					9 Months Ended		12 Months Ended						9 Months Ended																														0 Months Ended		9 Months Ended	0 Months Ended
	Jun. 19, 2013 Smart_meter	Sep. 30, 2014	Dec. 31, 2012	Sep. 18, 2014	Dec. 31, 2013	Sep. 30, 2014 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2008 Commonwealth Edison Co [Member]	Sep. 30, 2014 Commonwealth Edison Co [Member] Smart_meter	Sep. 30, 2013 Commonwealth Edison Co [Member]	Dec. 31, 2013 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Apr. 10, 2014 Commonwealth Edison Co [Member]	Mar. 19, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2010 Commonwealth Edison Co [Member]	Sep. 30, 2014 PECO Energy Co [Member] Smart_meter	Dec. 31, 2013 PECO Energy Co [Member]	Sep. 30, 2014 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	May 31, 2013 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Aug. 23, 2014 Baltimore Gas and Electric Company [Member]	Aug. 21, 2014 Baltimore Gas and Electric Company [Member]	Jul. 02, 2014 Baltimore Gas and Electric Company [Member]	Dec. 13, 2013 Baltimore Gas and Electric Company [Member]	May 17, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member] Smart_meter	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Dec. 31, 2013 Baltimore Gas and Electric Company [Member]	Sep. 15, 2014 Baltimore Gas and Electric Company [Member]	Jul. 02, 2014 Baltimore Gas and Electric Company [Member]	Feb. 26, 2014 Baltimore Gas and Electric Company [Member]	Aug. 23, 2013 Baltimore Gas and Electric Company [Member]	May 17, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]	Jun. 03, 2014 Exelon Generation Co L L C [Member] Minimum [Member]	Jun. 03, 2014 Exelon Generation Co L L C [Member] Maximum [Member]	Sep. 30, 2014 Under Recovered Distribution Service Costs [Member]	Dec. 31, 2013 Under Recovered Distribution Service Costs [Member]	Sep. 30, 2014 Under Recovered Distribution Service Costs [Member] Commonwealth Edison Co [Member]	Dec. 31, 2013 Under Recovered Distribution Service Costs [Member] Commonwealth Edison Co [Member]	Sep. 30, 2014 Under Recovered Distribution Service Costs [Member] PECO Energy Co [Member]	Dec. 31, 2013 Under Recovered Distribution Service Costs [Member] PECO Energy Co [Member]	Sep. 30, 2014 Under Recovered Distribution Service Costs [Member] Baltimore Gas and Electric Company [Member]	Dec. 31, 2013 Under Recovered Distribution Service Costs [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 AMI Expenses [Member]	Dec. 31, 2013 AMI Expenses [Member]	Sep. 30, 2014 AMI Expenses [Member] Commonwealth Edison Co [Member]	Dec. 31, 2013 AMI Expenses [Member] Commonwealth Edison Co [Member]	Sep. 30, 2014 AMI Expenses [Member] PECO Energy Co [Member]	Dec. 31, 2013 AMI Expenses [Member] PECO Energy Co [Member]	Sep. 30, 2014 AMI Expenses [Member] Baltimore Gas and Electric Company [Member]	Dec. 31, 2013 AMI Expenses [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2013 Energy Efficiency And Demand Response Programs [Member]	Sep. 30, 2014 Energy Efficiency And Demand Response Programs [Member] Commonwealth Edison Co [Member]	Dec. 31, 2013 Energy Efficiency And Demand Response Programs [Member] Commonwealth Edison Co [Member]	Sep. 30, 2014 Energy Efficiency And Demand Response Programs [Member] PECO Energy Co [Member]	Dec. 31, 2013 Energy Efficiency And Demand Response Programs [Member] PECO Energy Co [Member]	Sep. 30, 2014 Energy Efficiency And Demand Response Programs [Member] Baltimore Gas and Electric Company [Member]	Dec. 31, 2013 Energy Efficiency And Demand Response Programs [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Transmission Rate Formula [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Transmission Rate Formula [Member]	Dec. 31, 2013 Transmission Rate Formula [Member]	Jun. 19, 2014 FERC Transmission Complaint [Member] Baltimore Gas and Electric Company [Member]	Jun. 19, 2013 FERC Transmission Complaint [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 FERC Transmission Complaint [Member] Baltimore Gas and Electric Company [Member]	Oct. 15, 2014 Subsequent Event [Member] Commonwealth Edison Co [Member]	Oct. 17, 2014 Subsequent Event [Member] Baltimore Gas and Electric Company [Member]	Oct. 17, 2014 Subsequent Event [Member] Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Rate of Return on Common Equity, Incentive Basis Points		0.50%
Net regulatory asset																																						$ 466,000,000	$ 463,000,000																					$ 3,000,000	$ 19,000,000	$ 17,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																				24,000,000																																														269,000,000
Expected revenue adjustment for current year									174,000,000			80,000,000																																																						(20,000,000)
Expected revenue adjustment for prior year											95,000,000	7,000,000																																																						10,000,000
Requested Debt and Equity Return on Distribution									7.06%
Requested ROE									9.25%
Weighted Average Debt And Equity Return Electric Distribution									7.04%
Weighted Average Debt And Equity Return									8.62%	8.70%	9.20%														8.53%	8.35%
Public Utilities, Interim Rate Increase (Decrease), Amount																																																																		239,000,000
Approved Debt and Equity Rate on Distribution			7.54%
Approved ROE								10.30%				9.81%																																																					10.80%
ICC Approved Rate Increase (Decrease), Amount								274,000,000	73,000,000
Demand response peak demand reduction																			4.50%
Requested increase in electric revenues																													118,000,000			101,000,000
Adjustment to Requested increase in electric revenues																												99,000,000			83,000,000
Requested increase in gas revenues																													68,000,000			30,000,000
Rate of return on common equity electric distribution																							9.75%
Rate of return on common equity gas distribution																							9.60%
Increase in electric delivery service revenue resulting from rate case settlement or order.																											34,000,000																																									22,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.																											12,000,000																																									38,000,000
Annual Depreciation Expense Decrease Regulated Property																																																																			20,000,000
Requested Rate Of Return Common Equity Electric Distribution																						0.1065		0.105
Requested Rate Of Return Common Equity Gas Distribution																						0.1055		0.1035
Gross transmission revenue requirement						524,000,000				488,000,000															167,000,000		158,000,000
Transmission revenue true up						11,000,000	25,000,000																		4,000,000		1,000,000
Net transmission revenue requirement									535,000,000	513,000,000															171,000,000		157,000,000
Net Regulatory Asset																																						466,000,000	463,000,000																					3,000,000	19,000,000	17,000,000
Regulatory Rate of Return Approved																																																																	11.30%
Public Utilities, Interim Rate Increase (Decrease), Percentage																																																															10.57%
Public Utilities, Requested Rate Increase (Decrease), Percentage																																																																11.14%
Revenue Reduction																					10,000,000																																													30,000,000
Customer Refund Liability, Noncurrent				9,500,000									14,600,000	400,000	37,000,000						13,000,000
Estimated number of smart meters to be installed																1,600,000									2,000,000
Smart Meters Installed	600,000								500,000
Revised spend on its Smart Meter Procurement and Installation Plan																595,000,000
Spend on smart grid investments																120,000,000
Smart meter spend to date																516,000,000
Smart grid infrastructure spend to date																119,000,000
Total smart grid and smart meter investment grant amount																200,000,000
Smart meter investment grant awarded																140,000,000
Smart grid investment grant awarded																60,000,000
Reimbursements received from the DOE																200,000,000									200,000,000
Regulatory assets		5,589,000,000			5,910,000,000	928,000,000			928,000,000		933,000,000					1,520,000,000	1,448,000,000								500,000,000		524,000,000									223,000,000	285,000,000	223,000,000	285,000,000	0	0	0	0	254,000,000	159,000,000	69,000,000	35,000,000	74,000,000	58,000,000	111,000,000	66,000,000	151,000,000	148,000,000	0	0	0	0	151,000,000	148,000,000
Regulatory assets for original smart meters purchased																17,000,000
Vendor Refund																12,000,000
Amount of reimbursements received from the DOE applied to the originally installed Smart Meters.																16,000,000
Total Projected smart meter smart grid spend																									480,000,000
Current Year AMI Events Balance																	5,000,000
Depreciation Related To Original Meters																2,000,000
DOE Cash Payable to Sub Recipients																4,000,000
Upfront fee for opt-out of Smart Meter																														75
Recurring Fees																														11
Cumulative Consumption Reduction Targets																			3.00%
Proposed funding of estimated costs associated with DLC demand program due to modification of incentive levels for other Phase II programs.																		10,000,000
Customer Refund				9,500,000									14,600,000	400,000	37,000,000						13,000,000
Cash Collected									24,000,000
Rate Of Return On Common Equity						11.50%																			11.30%
Common Equity Component Cap									55.00%	11.50%
Capital and OM estimates current year																									14,800,000
Revenue Requirement																									1,400,000
Minimum Purchase Obligation																																		25,000,000
Maximum Purchase Obligation																																			35,000,000
License Costs																																	$ 38,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint																									8.70%
Transmission Rate Formula, First Basis Points Credited		0.50%