Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended																																																																				12 Months Ended					1 Months Ended	12 Months Ended																																																																			12 Months Ended		9 Months Ended	12 Months Ended																																																																					12 Months Ended			0 Months Ended		12 Months Ended
	Sep. 30, 2008	Dec. 31, 2012 MW		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 Nuclear Decommissioning [Member]	Dec. 31, 2011 Nuclear Decommissioning [Member]	Dec. 31, 2012 Removal Costs [Member]	Dec. 31, 2011 Removal Costs [Member]	Dec. 31, 2012 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2011 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2011 Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2011 Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2011 Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Regulatory Liabilities Other [Member]	Dec. 31, 2012 Gas Distribution Tax Repairs [Member]	Dec. 31, 2012 Pension and Other Postretirement Benefits [Member]	Dec. 31, 2011 Pension and Other Postretirement Benefits [Member]	Dec. 31, 2012 Deferred Income Taxes [Member]	Dec. 31, 2011 Deferred Income Taxes [Member]	Dec. 31, 2012 AMI Expenses [Member]	Dec. 31, 2011 AMI Expenses [Member]	Dec. 31, 2012 AMI Meter Events [Member]	Dec. 31, 2012 Under Recovered Distribution Service Costs [Member]	Dec. 31, 2011 Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Debt Costs [Member]	Dec. 31, 2011 Debt Costs [Member]	Dec. 31, 2012 Fair Value Of Long Term Debt [Member]		Dec. 31, 2012 Fair Value Of Supply Contract [Member]		Dec. 31, 2012 Severance [Member]	Dec. 31, 2011 Severance [Member]	Dec. 31, 2012 Asset Retirement Obligations [Member]	Dec. 31, 2011 Asset Retirement Obligations [Member]	Dec. 31, 2012 MGP Remediation Costs [Member]	Dec. 31, 2011 MGP Remediation Costs [Member]	Dec. 31, 2012 RTO Startup Costs [Member]	Dec. 31, 2011 RTO Startup Costs [Member]	Dec. 31, 2012 Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Financial Swap with Generation [Member]	Dec. 31, 2011 Financial Swap with Generation [Member]	Dec. 31, 2012 Renewable Energy And Associated REC [Member]	Dec. 31, 2011 Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 DSP Program costs [Member]	Dec. 31, 2012 DSP II Program Costs [Member]	Dec. 31, 2012 Deferred Storm Costs [Member]	Dec. 31, 2011 Deferred Storm Costs [Member]	Dec. 31, 2012 Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2011 Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Rate Stabilization Deferral [Member]	Dec. 31, 2011 Rate Stabilization Deferral [Member]	Dec. 31, 2012 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2011 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Other Regulatory Assets [Member]	Dec. 31, 2011 Other Regulatory Assets [Member]	Dec. 31, 2012 Regional Transmission Expansion Plan	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Nuclear Generation [Member] Salem [Member]	Sep. 30, 2008 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Removal Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Removal Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Regulatory Liabilities Other [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Gas Distribution Tax Repairs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] AMI Expenses [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] AMI Expenses [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] AMI Meter Events [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Debt Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Debt Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Fair Value Of Long Term Debt [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Fair Value Of Supply Contract [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Severance [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Severance [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] DSP Program costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] DSP II Program Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Minimum [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Maximum [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member] AlternativeEnergyCredits SmartMeters		Dec. 31, 2011 PECO Energy Co [Member]		Dec. 31, 2010 PECO Energy Co [Member]		Dec. 16, 2010 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 PECO Energy Co [Member] Removal Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Removal Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2011 PECO Energy Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Regulatory Liabilities Other [Member]	Dec. 31, 2012 PECO Energy Co [Member] Gas Distribution Tax Repairs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2011 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2012 PECO Energy Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2011 PECO Energy Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 PECO Energy Co [Member] AMI Expenses [Member]	Dec. 31, 2011 PECO Energy Co [Member] AMI Expenses [Member]	Dec. 31, 2012 PECO Energy Co [Member] AMI Meter Events [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Debt Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Debt Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Fair Value Of Long Term Debt [Member]		Dec. 31, 2012 PECO Energy Co [Member] Fair Value Of Supply Contract [Member]		Dec. 31, 2012 PECO Energy Co [Member] Severance [Member]	Dec. 31, 2011 PECO Energy Co [Member] Severance [Member]	Dec. 31, 2012 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2011 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 PECO Energy Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 PECO Energy Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 PECO Energy Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2011 PECO Energy Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 PECO Energy Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2011 PECO Energy Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 PECO Energy Co [Member] DSP Program costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] DSP II Program Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2011 PECO Energy Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2011 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2011 PECO Energy Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 PECO Energy Co [Member] Minimum [Member]	Dec. 31, 2012 PECO Energy Co [Member] Maximum [Member]	Dec. 31, 2012 PECO Energy Co [Member] Regional Transmission Expansion Plan	Jun. 01, 2013 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Jul. 27, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] MW SmartMeters		Dec. 31, 2011 Baltimore Gas and Electric Company [Member]		Dec. 31, 2010 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Regulatory Liabilities Other [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Gas Distribution Tax Repairs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Deferred Income Taxes [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] AMI Meter Events [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Fair Value Of Long Term Debt [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Fair Value Of Supply Contract [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Severance [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Severance [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Asset Retirement Obligations [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] MGP Remediation Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] RTO Startup Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] RTO Startup Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Financial Swap with Generation [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] DSP Program costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] DSP II Program Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Deferred Storm Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Other Regulatory Assets [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Regional Transmission Expansion Plan
Operating And Maintenance For Regulatory Required Programs [Line Items]
Total operating and maintenance for regulatory required programs
Purchase Of Receivables [Abstract]
POR gross receivables		191.00	[1]	68.00	[1]																																																																							55.00	[1]	16.00	[1]																																																																			65.00	[1]	52.00	[1]																																																																							71.00	[1]	61.00	[1]
POR Allowance for uncollectible accounts		(21.00)	[2]	(5.00)	[2]																																																																							(9.00)	[2]	0	[2]																																																																			(6.00)	[2]	(5.00)	[2]																																																																							(6.00)	[2]	(3.00)	[2]
POR net receivables		170.00		63.00																																																																								46.00		16.00																																																																				59.00		47.00																																																																								65.00		58.00
Rate Relief Costs [Line Items]
Credits to ComEd customers				15.00	[3]																																																																		14.00	[3]						1.00	[3]
Credits to other Illinois utilities' customers																																																																							7.00	[3]
Total incurred costs				15.00																																																																			21.00							1.00
Energy Infrastructure Modernization Act [Abstract]
Additional investment to modernize system and implement smart grid technology.																																																																												2.60
Annual contribution to fund customer assistance programs																																																																												10.00
Contribution to a science and technology innovation trust																																																																												15.00
Subsequent annual contributions to the trust																																																																												4.00
Current length of state legislation enacted																																																																												10 years
Planned capital spend by a utility under state enacted legislation																																																																												233.00
Annual revenue requirement reduction																																																																												168.00
Annual revenue requirement reduction incremental to proposal																																																																												110.00
Annual revenue requirement incremental reduction attributable to alternative recovery																																																																												50.00
Annual revenue requirement incremental reduction attributable to pensions																																																																												35.00
Annual revenue requirement incremental reduction attributable to incentives																																																																												10.00
Annual revenue requirement incremental reduction attributable to other adjustments																																																																												15.00
Regulatory asset reduction due to final order																																																																												100.00
Over or Under recovered distribution service costs																																																																												125.00
Under recovered distribution service costs related to one time events																																																																												84.00
Deferral of AMI plan																																																																												50.00
Deferral of additional capital investment																																																																												15.00
Regulatory asset for the accelerated depreciation of non-AMI meters																																																																												7.00
Increased revenue requirement																																																																												73.00
Expected revenue adjustment in subsequent quarter																																																																												135.00
Expected revenue adjustment for prior year																																																																												75.00
Expected revenue adjustment for current year																																																																												60.00
Regulatory assets due to deferred storm costs																																																																												58.00
Regulatory assets due to merger and integration-related costs																																																																												26.00
Other regulatory assets due to merger and integration-related costs																																																																												5.00																																																																																																																																																1.00
Illinois Settlement Agreement [Abstract]
Overall rate relief contribution		1,000.00																																																																							747.00
Rate relief to ComEd customers																																																																									435.00							64.00
Rate relief to other Illinois Utilities																																																																									308.00
Contribution to IPA																																																																									5.00
Annual energy savings requirement																																																																												0.20%																																																																																																																																														3.00%
Demand response peak demand reduction																																																																												2.00%																																																																																																																																														4.50%
Renewable energy procurement																																																																												2.00%
Distribution Rate Case [Abstract]
Requested increase in electric revenues																																																																																396.00																																																																																																																																											131.00
Adjustment to Requested increase in electric revenues																																																																																343.00
Recovery request for Operating and Maintenance expenses of AMI Pilot Program																																																																												40.00
Requested increase in gas revenues																																																																																																																																																																																																																											45.00
Requested rate of return on common equity																																																																												11.50%																																																																																																																																															10.50%
Rate of return on common equity electric distribution																																																																											10.30%	10.50%
Intervenor potential refund submitted in testimony																																																																											37.00
Increase in electric delivery service revenue resulting from rate case settlement																																																																												143.00																																																																												225.00
Increase in gas delivery service revenue resulting from rate case settlement																																																																																																																																																								20.00
ComEd's proposed increase to net distribution revenue requirement related to uncollectable account expense																																																																												22.00
Electric Distribution Tax Repairs Refund																																																																																																																																																		171.00
Appeal of 2007 Illinois Electric Distribution Rate Case [Abstract]
Increase in electric delivery service revenue requirement resulting from regulatory order in rate case	274.00
Utility Consolidated Billing and Purchase of Receivables [Abstract]
Purchased AR associated with PORCB																																																																												55.00
Illinois Procurement Proceedings [Abstract]
Near zero emissions coal-fueled generation plant		166
Illinois Legislation for Recovery of Uncollectible Accounts [Abstract]
Under-collected uncollectible accounts regulatory asset																																																																												70.00
One-time operating and maintenance expense charge																																																																												10.00
Annual Transmission Formula Rate Update [Abstract]
Gross transmission revenue requirement																																																																												450.00		438.00																																																																																																																																														156.00
Transmission revenue true up																																																																												5.00		16.00																																																																																																																																														2.00
Net transmission revenue requirement																																																																												445.00		422.00																																																																																																																																														158.00		140.00
PJM Transmission Rate Design And Operating Agreements Abstract
Total construction commitments																																																																					(525.00)																																																																																																																																																				(140.00)																																																																						(249.00)
Construction commitments due in next twelve months																																																																					(175.00)																																																																																																																																																				(28.00)																																																																						(15.00)
Construction commitments due in second year																																																																					(86.00)																																																																																																																																																				(23.00)																																																																						(53.00)
Construction commitments due in third year																																																																					(135.00)																																																																																																																																																				(26.00)																																																																						(119.00)
Construction commitments due in fourth year																																																																					(128.00)																																																																																																																																																				(36.00)																																																																						(55.00)
Construction commitments due in five year																																																																					(1.00)																																																																																																																																																				(27.00)																																																																						(7.00)
Smart Meter and Smart Grid Investments [Abstract]
Estimated number of smart meters to be installed																																																																																																																																																		600,000																																																																										2,000,000
Expected number of smart meters to be deployed during the first phase of Smart Meter Installment Plan																																																																																																																																																		1.60
Revised spend on its Smart Meter Procurement and Installation Plan																																																																																																																																																		595.00
Spend on smart grid investments																																																																																																																																																		120.00
Smart meter spend to date																																																																																																																																																		241.00
Smart grid infrastructure spend to date																																																																																																																																																		100.00
Total smart grid and smart meter investment grant amount																																																																																																																																																		200.00																																																																										200.00
Smart meter investment grant awarded																																																																																																																																																		140.00
Smart grid investment grant awarded																																																																																																																																																		60.00
Reimbursements received from the DOE																																																																																																																																																		144.00																																																																										142.00
Outstanding reimbursable DOE Smart Grid Investment Grant expenditures																																																																																																																																																		17.00																																																																										15.00
Regulatory assets for original smart meters purchased																																																																																																																																																		17.00
Carrying value of originally installed Smart Meters, net of reimbursements from DOE																																																																																																																																																		19.00
Amount of reimbursements received from the DOE applied to the originally installed Smart Meters.																																																																																																																																																		16.00
Total Projected smart meter smart grid spend																																																																																																																																																																																																																												480.00
New Electric Generation [Abstract]
Megawatt capacity of new generating plant																																																																																																																																																																																																																												700
Energy Efficiency Program [Abstract]
Maximum civil penalty under Act 129																																																																																																																																																																																																																										20.00
Total approved amount under energy efficiency and conservation / demand plan																																																																																																																																																																																																																										328.00
Cumulative Consumption Reduction Targets																																																																																																																																																																																																																										2.90%
Consumption reduction target (as a percentage) mandated by the Energy Efficiency Program - Phase II Implemtation Order for programs directed towards the Utility's low income sector.																																																																																																																																																																																																																										4.50%
Consumption reduction targets for public sector under Act 129 Phase II Implementation Order																																																																																																																																																																																																																										10.00%
Total approved amount under phase II of Act 129 as percent of total annual revenue																																																																																																																																																																																																																										2.00%
Renewable energy resources that will cumulatively increase																																																																																																																																															10.00%	25.00%
Advanced metering infrastructure pilot program [Abstract]
Collections Under Rider Amp																																																																														24.00
Alternative Energy Portfolio Standards [Abstract]
Percentage Tier I alternative energy resources																																																																																																																																																																																																																							3.50%	8.00%
Percentage Tier II alternative energy resources																																																																																																																																																																																																																							6.20%	10.00%
Total alternative energy credits purchased annually																																																																																																																																																		452,000
Solar tier 1 alternative energy credits purchased annually																																																																																																																																																		8,000
Tier II AECs Purchased																																																																																																																																																		275,000
Natural Gas Distribution Rate Case [Abstract]
Gas Distribution Tax Repairs Refund																																																																																																																																																	54.00
Authorized Return On Rate Base [Abstract]
Weighted Average Debt And Equity Return																																																																												8.91%		9.10%																																																																																																																																														8.43%		8.96%
Rate Of Return On Common Equity																																																																												11.50%																																																																																																																																																11.30%
Common Equity Component Cap																																																																												55.00%
Regulatory Assets And Liabilities Other Disclosures [Abstract]
Pension and other postretirement benefit regulatory asset held at parent company		3,977.00
Over under recovered transmission costs																																																																																																																																																		1.00		9.00
Over under recovered electric supply costs																																																																																																																																																		47.00		25.00																																																																								(9.00)
Over under recovered gas supply costs																																																																																																																																																		1.00		5.00																																																																								(19.00)
Amortization of rate stabilization deferral		57.00		57.00																																																																																																																																																																																																																								67.00		57.00		62.00
Total cost of smart grid pilot program																																																																																																																																																																																																																												11.00
Portion of electric generation-related regulatory asset representing income taxes recoverable that do not earn a regulated rate of return																																																																																																																																																																																																																												47.00		56.00
Rate cap for BGE residential electric customers from July 1, 2006 until May 31, 2007 (as a percent)																																																																																																																																																																																																																												15.00%
Deferred expense related to electricity purchased for resale																																																																																																																																																																																																																												306.00
Recovered portion of regulatory assets		129.00		63.00		931.00																																																																0	0		0			80.00		52.00		43.00																																																																		10.00		11.00	[4]	889.00	[4]																																																																					53.00		50.00		35.00
Ownership of Salem Units		99.00%
Equity Ratio Minimum After Dividend Payments																																																																																																																																																																																																																												48.00%
Natural Gas Supplier Tariff [Abstract]
Natural gas supplier tariff total collateral																																																																																																																																																		14.00
Maryland Electric And Natural Gas Distribution Rate Cases [Abstract]
Deferral of total costs																																																																																																																																																																																																																												19.00
Deferral of storm costs																																																																																																																																																																																																																												16.00		(16.00)
License Renewals [Abstract]
Ownership interest																																																																										42.59%
Regulatory Asset [Line Items]
Noncurrent regulatory assets		6,497.00		4,518.00																					3,673.00	2,794.00	1,382.00	1,176.00	70.00	28.00	17.00	191.00	70.00	68.00	81.00	256.00	[5]	12.00	[6]	28.00	38.00	90.00	74.00	232.00	129.00	2.00	4.00	0	0	0	0	49.00	97.00	0	0	2.00	3.00	2.00	6.00	0	40.00	0	225.00	0	126.00	0	25.00	25.00								666.00		699.00																					0	0	62.00	66.00	10.00	6.00	0	191.00	70.00	62.00	73.00	0	[5]	0	[6]	12.00	38.00	65.00	50.00	197.00	91.00	2.00	4.00	0	0	0	191.00	49.00	97.00	0	0	0	0	0	0	0	0	0	0	0	0	0	16.00	13.00				1,378.00		1,216.00																							0	0	1,255.00	1,110.00	29.00	22.00	17.00	0	0	6.00	8.00	0	[5]	0	[6]	0	0	25.00	24.00	33.00	38.00	0	0	0	0	0	0	0	0	0	0	2.00	3.00	2.00	0	0	0	0	0	0	0	0	8.00	12.00						522.00		551.00																					0	0	65.00	68.00	31.00	15.00	0	0	0	9.00	10.00	0	[5]	0	[6]	16.00	1.00	0	0	2.00	2.00	0	0	0	0	0	0	0	0	0	0	0	0	0	6.00	9.00	40.00	56.00	225.00	295.00	126.00	95.00	2.00	0
Current regulatory assets		759.00		390.00																					304.00	204.00	14.00	5.00	3.00	2.00	0	18.00	14.00	14.00	18.00	0	[5]	77.00	[6]	29.00	25.00	0	0	58.00	30.00	3.00	3.00	11.00	3.00	0	0	18.00	9.00	43.00	57.00	3.00	1.00	1.00	3.00	0	16.00	0	67.00	0	56.00	0	23.00	17.00								388.00		657.00																					0	0	5.00	5.00	3.00	2.00	0	18.00	14.00	11.00	15.00	0	[5]	0	[6]	25.00	25.00	0	0	51.00	24.00	3.00	3.00	0	0	226.00	503.00	18.00	9.00	14.00	48.00	0	0	0	0	0	0	0	0	0	0	0	14.00	9.00				32.00		39.00																							0	7.00	0	0	0	0	0	0	0	3.00	3.00	0	[5]	0	[6]	0	0	0	0	6.00	6.00	0	0	11.00	3.00	0	0	0	0	1.00	9.00	3.00	1.00	1.00	0	0	0	0	0	0	0	0	9.00	8.00						185.00		175.00																					0	3.00	9.00	8.00	0	0	0	0	0	1.00	2.00	0	[5]	0	[6]	4.00	0	0	0	1.00	1.00	0	0	0	0	0	0	0	0	28.00	50.00	0	0	0	3.00	3.00	16.00	16.00	67.00	63.00	56.00	29.00	0	0
Net regulatory asset																																																																																																																				209.00	84.00
Regulatory Liabilities [Line Items]
Regulatory Liability Current		321.00		197.00			0	0	97.00	61.00	131.00	49.00	20.00	19.00	6.00	15.00	54.00	42.00	3.00	3.00	2.00	8.00	0	8.00																																																				130.00		137.00			0	0	75.00	61.00	43.00	49.00	0	0	6.00	15.00	6.00	12.00	0	0	0	0	0																																																	169.00		60.00					0	0	0	0	88.00	0	20.00	19.00	0	0	48.00	30.00	3.00	3.00	2.00	8.00	0	8.00																																																		22.00		19.00			0	0	22.00	18.00	0	0	0	0	0	0	0	0	0	0	0	0	1.00
Noncurrent regulatory liabilities		$ 3,981.00		$ 3,627.00			$ 2,397.00	$ 2,222.00	$ 1,406.00	$ 1,185.00	$ 0	$ 69.00	$ 132.00	$ 151.00	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 46.00																																																				$ 3,229.00		$ 3,042.00			$ 2,037.00	$ 1,857.00	$ 1,192.00	$ 1,185.00	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0																																																	$ 538.00		$ 585.00					$ 360.00	$ 365.00	$ 0	$ 0	$ 0	$ 69.00	$ 132.00	$ 151.00	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 46.00																																																		$ 214.00		$ 201.00			$ 0	$ 0	$ 214.00	$ 200.00	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1.00

[1] PECO's gas POR program became effective on January 1, 2012 and includes a 1% discount on purchased receivables in order to recover the implementation costs of the program. If the costs are not fully recovered when PECO files its next gas distribution rate case, PECO will propose a mechanism to recover the remaining implementation costs as a distribution charge to low volume transportation customers or apply future discounts on purchased receivables from natural gas suppliers serving those customers.

[2] For ComEd, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing (PORCB) tariff.

[3] Recorded as a reduction in operating revenues.

[4] For PECO, primarily reflects CTC amortization.

[5] Represents the regulatory asset recorded at Exelon Corporate for the difference in the fair value of the long-term debt of BGE as of the merger date. See Note 4 – Merger and Acquisitions for additional information.

[6] Represents the regulatory asset recorded at Exelon Corporate representing the fair value of BGE’s supply contracts as of the merger date. BGE is allowed full recovery of the costs of its electric and gas supply contracts through approved regulated rates. See Note 4 – Merger and Acquisitions for additional information.