Regulatory Matters (Details) (USD $)	3 Months Ended																																																																																								1 Months Ended	3 Months Ended			12 Months Ended																																																																					3 Months Ended																																																																											0 Months Ended	3 Months Ended				12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012		Mar. 31, 2013 Nuclear Decommissioning [Member]	Dec. 31, 2012 Nuclear Decommissioning [Member]	Mar. 31, 2013 Removal Costs [Member]	Dec. 31, 2012 Removal Costs [Member]	Mar. 31, 2013 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Energy Efficiency Demand Response Programs [Member]	Mar. 31, 2013 Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Electric Transmission And Distribution Tax Repairs [Member]	Mar. 31, 2013 Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Over Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Over Recovered Energy And Transmission Costs [Member]	Mar. 31, 2013 Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Over-Recovered Universal Service Fund Costs [Member]	Mar. 31, 2013 Over-Recovered AEPS Costs [Member]	Dec. 31, 2012 Over-Recovered AEPS Costs [Member]	Mar. 31, 2013 Revenue subject to refund [Member]		Dec. 31, 2012 Revenue subject to refund [Member]		Mar. 31, 2013 Over Recovered Decoupling Revenue [Member]		Dec. 31, 2012 Over Recovered Decoupling Revenue [Member]		Dec. 31, 2012 Gas Distribution Tax Repairs [Member]	Mar. 31, 2013 Regulatory Liabilities Other [Member]	Mar. 31, 2013 Pension and Other Postretirement Benefits [Member]		Dec. 31, 2012 Pension and Other Postretirement Benefits [Member]		Mar. 31, 2013 Deferred Income Taxes [Member]	Dec. 31, 2012 Deferred Income Taxes [Member]	Mar. 31, 2013 AMI Expenses [Member]	Dec. 31, 2012 AMI Expenses [Member]	Mar. 31, 2013 AMI Meter Events [Member]	Dec. 31, 2012 AMI Meter Events [Member]	Mar. 31, 2013 Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Under Recovered Distribution Service Costs [Member]	Mar. 31, 2013 Debt Costs [Member]	Dec. 31, 2012 Debt Costs [Member]	Mar. 31, 2013 Fair Value Of Long Term Debt [Member]		Dec. 31, 2012 Fair Value Of Long Term Debt [Member]		Mar. 31, 2013 Fair Value Of Supply Contract [Member]		Dec. 31, 2012 Fair Value Of Supply Contract [Member]		Mar. 31, 2013 Severance [Member]	Dec. 31, 2012 Severance [Member]	Mar. 31, 2013 Asset Retirement Obligations [Member]	Dec. 31, 2012 Asset Retirement Obligations [Member]	Mar. 31, 2013 MGP Remediation Costs [Member]	Dec. 31, 2012 MGP Remediation Costs [Member]	Mar. 31, 2013 RTO Startup Costs [Member]	Dec. 31, 2012 RTO Startup Costs [Member]	Mar. 31, 2013 Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Under Recovered Universal Service Fund Costs Member [Member]	Mar. 31, 2013 Under Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 Financial Swap with Generation [Member]	Dec. 31, 2012 Financial Swap with Generation [Member]	Mar. 31, 2013 Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Renewable Energy And Associated REC [Member]	Mar. 31, 2013 Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Under Recovered Energy And Transmission Costs [Member]	Mar. 31, 2013 DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2013 DSP II Program Electric Procurement Contracts [Member]	Dec. 31, 2012 DSP Program costs [Member]	Dec. 31, 2012 DSP II Program Costs [Member]	Mar. 31, 2013 Deferred Storm Costs [Member]	Dec. 31, 2012 Deferred Storm Costs [Member]	Mar. 31, 2013 Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Electric Generation Related Regulatory Asset [Member]	Mar. 31, 2013 Rate Stabilization Deferral [Member]	Dec. 31, 2012 Rate Stabilization Deferral [Member]	Mar. 31, 2013 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Under Recovered Decoupling Revenue [Member]		Mar. 31, 2013 Merger Integration Costs [Member]		Mar. 31, 2013 Other Regulatory Assets [Member]	Dec. 31, 2012 Other Regulatory Assets [Member]	Sep. 30, 2008 Commonwealth Edison Co [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Removal Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Removal Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Revenue subject to refund [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Revenue subject to refund [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] AMI Expenses [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] AMI Expenses [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Distribution Service Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Debt Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Debt Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Fair Value Of Long Term Debt [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Fair Value Of Supply Contract [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member] Severance [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Severance [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Under Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Renewable Energy And Associated REC [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] DSP II Program Electric Procurement Contracts [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Electric Generation Related Regulatory Asset [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Energy Efficiency And Demand Response Programs [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Mar. 31, 2013 PECO Energy Co [Member] SmartMeters		Mar. 31, 2012 PECO Energy Co [Member]	Dec. 31, 2012 PECO Energy Co [Member]		Mar. 31, 2013 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Mar. 31, 2013 PECO Energy Co [Member] Removal Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Removal Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]		Dec. 31, 2012 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]		Mar. 31, 2013 PECO Energy Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Gas Distribution Tax Repairs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Gas Distribution Tax Repairs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Regulatory Liabilities Other [Member]	Mar. 31, 2013 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]		Dec. 31, 2012 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]		Mar. 31, 2013 PECO Energy Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 PECO Energy Co [Member] Deferred Income Taxes [Member]	Mar. 31, 2013 PECO Energy Co [Member] AMI Expenses [Member]	Dec. 31, 2012 PECO Energy Co [Member] AMI Expenses [Member]	Mar. 31, 2013 PECO Energy Co [Member] AMI Meter Events [Member]	Dec. 31, 2012 PECO Energy Co [Member] AMI Meter Events [Member]	Mar. 31, 2013 PECO Energy Co [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Distribution Service Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Debt Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Debt Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Fair Value Of Long Term Debt [Member]		Mar. 31, 2013 PECO Energy Co [Member] Fair Value Of Supply Contract [Member]		Mar. 31, 2013 PECO Energy Co [Member] Severance [Member]	Dec. 31, 2012 PECO Energy Co [Member] Severance [Member]	Mar. 31, 2013 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Mar. 31, 2013 PECO Energy Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] MGP Remediation Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] RTO Startup Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Universal Service Fund Costs Member [Member]	Mar. 31, 2013 PECO Energy Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 PECO Energy Co [Member] Financial Swap with Generation [Member]	Mar. 31, 2013 PECO Energy Co [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 PECO Energy Co [Member] Renewable Energy And Associated REC [Member]	Mar. 31, 2013 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]		Mar. 31, 2013 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2013 PECO Energy Co [Member] DSP II Program Electric Procurement Contracts [Member]	Dec. 31, 2012 PECO Energy Co [Member] DSP II Program Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Deferred Storm Costs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 PECO Energy Co [Member] Electric Generation Related Regulatory Asset [Member]	Mar. 31, 2013 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Mar. 31, 2013 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 PECO Energy Co [Member] Other Regulatory Assets [Member]	Jun. 01, 2013 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Mar. 31, 2013 PECO Energy Co [Member] Energy Efficiency And Demand Response Programs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] MW SmartMeters		Mar. 31, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Energy Efficiency Demand Response Programs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Electric Transmission And Distribution Tax Repairs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Energy And Transmission Costs [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Energy And Transmission Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Gas Energy And Transmission Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over-Recovered Universal Service Fund Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over-Recovered AEPS Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Decoupling Revenue [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Decoupling Revenue [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Decoupling Electric Revenue [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Over Recovered Decoupling Gas Revenue [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Over Recovered Decoupling Gas Revenue [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Regulatory Liabilities Other [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Pension and Other Postretirement Benefits [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Pension and Other Postretirement Benefits [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Deferred Income Taxes [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Deferred Income Taxes [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Under Recovered Distribution Service Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Distribution Service Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Fair Value Of Long Term Debt [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Fair Value Of Supply Contract [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Severance [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Severance [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Asset Retirement Obligations [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Asset Retirement Obligations [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] MGP Remediation Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] MGP Remediation Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] RTO Startup Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] RTO Startup Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Universal Service Fund Costs Member [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Financial Swap with Generation [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Financial Swap with Generation [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Renewable Energy And Associated REC [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Renewable Energy And Associated REC [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Energy And Transmission Costs [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Electric Energy And Transmission Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Gas Energy And Transmission Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] DSP II Program Electric Procurement Contracts [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Deferred Storm Costs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Deferred Storm Costs [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Electric Generation Related Regulatory Asset [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Rate Stabilization Deferral [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Decoupling Revenue [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Under Recovered Decoupling Electric Revenue [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Merger Integration Costs [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Other Regulatory Assets [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Other Regulatory Assets [Member]	Mar. 31, 2013 Exelon Corporate [Member] Gas Distribution Tax Repairs [Member]
Purchase Of Receivables [Abstract]
POR gross receivables	$ 244,000,000	[1]		$ 191,000,000	[1]																																																																																					$ 86,000,000	[1]		$ 55,000,000	[1]																																																																				$ 69,000,000	[1]		$ 65,000,000	[1]																																																																									$ 89,000,000	[1]		$ 71,000,000	[1]
POR Allowance for uncollectible accounts	(25,000,000)	[2]		(21,000,000)	[2]																																																																																					(13,000,000)	[2]		(9,000,000)	[2]																																																																				(7,000,000)	[2]		(6,000,000)	[2]																																																																									(5,000,000)	[2]		(6,000,000)	[2]
POR net receivables	219,000,000			170,000,000																																																																																						73,000,000			46,000,000																																																																					62,000,000			59,000,000																																																																										84,000,000			65,000,000
Energy Infrastructure Modernization Act [Abstract]
Additional investment to modernize system and implement smart grid technology.																																																																																										2,600,000,000
Annual contribution to fund customer assistance programs																																																																																										10,000,000
Contribution to a science and technology innovation trust																																																																																										15,000,000
Subsequent annual contributions to the trust																																																																																										4,000,000
Current length of state legislation enacted			10 years
Planned capital spend by a utility under state enacted legislation																																																																																										233,000,000
Deferral of AMI plan																																																																																										50,000,000
Deferral of additional capital investment																																																																																										15,000,000
Increased revenue requirement																																																																																										311,000,000
Expected revenue adjustment for prior year																																																																																										142,000,000
Expected revenue adjustment for current year																																																																																										169,000,000
Excess basis points over treasury after year one																																																																																										5.80%
Senate Bill [Abstract]
Next 12 months Projected Revenue	25,000,000
Year 2 Projected Revenue	65,000,000
Next 12 months Projected CapEx	35,000,000
Year 2 Projected CapEx	40,000,000
Illinois Settlement Agreement [Abstract]
Annual energy savings requirement																																																																																																																																																																																																																																														3.00%
Demand response peak demand reduction																																																																																																																																																																																																																																													4.50%
Distribution Rate Case [Abstract]
Rate of return on common equity electric distribution																																																																																									0.103%																																																																																																																																																						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.																																																																																																																																																																																																																																															81,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.																																																																																																																																																																																																																																															32,000,000
Regulatory Assets Transfer Changes																																																																																																																																																																																																																																															8,000,000
Regulatory Assets Prior Period Transfer Changes																																																																																																																																																																																																																																															6,000,000
Severance Recovered Through Distribution Rates																																																																																																																																																																																																																																															20,000,000
Appeal of 2007 Illinois Electric Distribution Rate Case [Abstract]
Increase in electric delivery service revenue requirement resulting from regulatory order in rate case																																																																																									274,000,000
Annual Transmission Formula Rate Update [Abstract]
Gross transmission revenue requirement																																																																																										488,000,000		450,000,000																																																																																																																																																			158,000,000			156,000,000
Transmission revenue true up																																																																																										25,000,000		5,000,000																																																																																																																																																			1,000,000			2,000,000
Net transmission revenue requirement																																																																																										513,000,000		445,000,000																																																																																																																																																			157,000,000			158,000,000
Smart Meter and Smart Grid Investments [Abstract]
Estimated number of smart meters to be installed																																																																																																																																																																		1,600,000																																																																													2,000,000
Expected number of smart meters to be deployed during the first phase of Smart Meter Installment Plan																																																																																																																																																																		600,000
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																																																																																																																																																																		262,000,000
Smart grid infrastructure spend to date																																																																																																																																																																		103,000,000
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																																																																													200,000,000
Reimbursements received from the DOE																																																																																																																																																																		161,000,000																																																																													162,000,000
Outstanding reimbursable DOE Smart Grid Investment Grant expenditures																																																																																																																																																																		8,000,000																																																																													13,000,000
Regulatory assets for original smart meters purchased																																																																																																																																																																		17,000,000
Carrying value of originally installed Smart Meters, net of reimbursements from DOE																																																																																																																																																																		19,000,000
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
New Electric Generation [Abstract]
Megawatt capacity of new generating plant																																																																																																																																																																																																																																															700
Energy Efficiency Program [Abstract]
Cumulative Consumption Reduction Targets																																																																																																																																																																																																																																													2.90%
Amount of cost recoveries sought under the Direct Load Control Program.																																																																																																																																																																																																																																														12,000,000
Proposed funding of estimated costs associated with DLC demand program due to modification of incentive levels for other Phase II programs.																																																																																																																																																																																																																																														20,000,000
Advanced metering infrastructure pilot program [Abstract]
Collections Under Rider Amp																																																																																													24,000,000
Authorized Return On Rate Base [Abstract]
Weighted Average Debt And Equity Return Electric Distribution																																																																																													0.0699%		0.0701%
Weighted Average Debt And Equity Return																																																																																										8.70%		8.91%																																																																																																																																																			8.35%		8.43%
Rate Of Return On Common Equity																																																																																										11.50%			0.0872%		0.0872%																																																																																																																																																10.80%			11.30%
Rate Of Return On Common Equity in FERC Complaint																																																																																																																																																																																																																																															8.70%
Potential refund resulting from the FERC Comlaint																																																																																																																																																																																																																																															10,000,000
Common Equity Component Cap																																																																																										55.00%
Regulatory Assets And Liabilities Other Disclosures [Abstract]
Over under recovered transmission costs																																																																																																																																																																		6,000,000
Over under recovered electric supply costs																																																																																																																																																																		39,000,000			47,000,000
Over under recovered gas supply costs																																																																																																																																																																		26,000,000			1,000,000
Amortization of rate stabilization deferral	30,000,000		3,000,000																																																																																																																																																																																																																																												30,000,000		13,000,000
Recovered portion of regulatory assets	61,000,000		25,000,000																																																																																							30,000,000		18,000,000																																																																						2,000,000		2,000,000																																																																											29,000,000		18,000,000
Maryland Electric And Natural Gas Distribution Rate Cases [Abstract]
Deferral of storm costs																																																																																																																																																																																																																																																	0
Regulatory Asset [Line Items]
Noncurrent regulatory assets	6,521,000,000			6,497,000,000																												3,685,000,000	[3]	3,673,000,000	[3]	1,397,000,000	1,382,000,000	81,000,000	70,000,000	17,000,000	17,000,000	203,000,000	191,000,000	65,000,000	68,000,000	245,000,000	[4]	256,000,000	[4]	9,000,000	[5]	12,000,000	[5]	23,000,000	28,000,000	92,000,000	90,000,000	223,000,000	232,000,000	2,000,000	2,000,000	0	0		0	0	60,000,000	49,000,000	0	0	3,000,000	2,000,000	3,000,000	2,000,000	5,000,000	6,000,000	40,000,000	40,000,000	209,000,000	225,000,000	129,000,000	126,000,000			7,000,000	[6]	24,000,000	25,000,000		681,000,000			666,000,000																							0	[3]	0	[3]	63,000,000	62,000,000	16,000,000	10,000,000	203,000,000	191,000,000	60,000,000	62,000,000	0	[4]	0	[5]	6,000,000	12,000,000	67,000,000	65,000,000	189,000,000	197,000,000	2,000,000	2,000,000	0	0		0	0	60,000,000	49,000,000	0	0	0	0	0	0	0	0	0	0	0	0	0	15,000,000	16,000,000	1,389,000,000			1,378,000,000																							0	[3]	0	[3]	1,269,000,000	1,255,000,000	28,000,000	29,000,000	17,000,000	17,000,000	0	0	5,000,000	6,000,000	0	[4]	0	[5]	0	0	25,000,000	25,000,000	32,000,000	33,000,000	0	0	0	0	0	0	0	0	0	0		3,000,000	3,000,000	2,000,000	2,000,000	0	0	0	0	0		0	0	8,000,000	8,000,000			522,000,000			522,000,000																												0	[3]	0	[3]	65,000,000	65,000,000	37,000,000	31,000,000	0	0	9,000,000	9,000,000	0	[4]	0	[5]	17,000,000	16,000,000	0	0	2,000,000	2,000,000	0	0	0	0	0	0	0	0	0	0				0	0	0	5,000,000	6,000,000	40,000,000	40,000,000	209,000,000	225,000,000	129,000,000	126,000,000				7,000,000	[6]	2,000,000	2,000,000
Current regulatory assets	765,000,000			764,000,000																												308,000,000	[3]	304,000,000	[3]	14,000,000	14,000,000	3,000,000	3,000,000			52,000,000	18,000,000	13,000,000	14,000,000	0	[4]			61,000,000	[5]	77,000,000	[5]	29,000,000	29,000,000	0	0	56,000,000	58,000,000	3,000,000	3,000,000	4,000,000	11,000,000	6,000,000	0	0	15,000,000	18,000,000	32,000,000	43,000,000	1,000,000	2,000,000	1,000,000	1,000,000	3,000,000	3,000,000	13,000,000	16,000,000	67,000,000	67,000,000	49,000,000	56,000,000	5,000,000	[7]	1,000,000	[6]	33,000,000	23,000,000		301,000,000			388,000,000																							0	[3]	0	[3]	5,000,000	5,000,000	3,000,000	3,000,000	52,000,000	18,000,000	10,000,000	11,000,000	0	[4]	0	[5]	25,000,000	25,000,000	0	0	49,000,000	51,000,000	3,000,000	3,000,000	0	0	6,000,000	85,000,000	226,000,000	15,000,000	18,000,000	32,000,000	14,000,000	0	0	0	0	0	0	0	0	0	0	0	16,000,000	14,000,000	33,000,000			32,000,000																							0	[3]	0	[3]	0	0	0	0			0	0	3,000,000	3,000,000	0	[4]	0	[5]	0	0	0	0	6,000,000	6,000,000	0	0	4,000,000	11,000,000	0	0	0	0	0	1,000,000	[8]	1,000,000	1,000,000	2,000,000	1,000,000	0	0	0	0	0	0	0	0	17,000,000	9,000,000			148,000,000			190,000,000																												0	[3]	0	[3]	9,000,000	9,000,000	0	0	0	0	1,000,000	1,000,000	0	[4]	0	[5]	4,000,000	4,000,000	0	0	1,000,000	1,000,000	0	0	0	0	0	0	0	0	0	28,000,000	[9]	9,000,000	19,000,000	0	0	0	3,000,000	3,000,000	13,000,000	16,000,000	67,000,000	67,000,000	49,000,000	56,000,000	5,000,000	[7]	5,000,000	1,000,000	[6]	0	0
Net regulatory asset																																																																																																																												255,000,000	209,000,000
Regulatory Liabilities [Line Items]
Regulatory Liability Current	418,000,000			368,000,000		0	0	98,000,000	97,000,000	145,000,000	131,000,000	20,000,000	20,000,000	0	6,000,000	85,000,000	54,000,000	3,000,000	3,000,000	1,000,000	2,000,000	40,000,000	[10]	40,000,000	[10]	15,000,000	[7]	7,000,000	[7]	8,000,000	3,000,000																																																											166,000,000			170,000,000			0	0	77,000,000	75,000,000	43,000,000	43,000,000	0	0	0	6,000,000	6,000,000	6,000,000	0	0	0	0	40,000,000	[10]	40,000,000	[10]																																															205,000,000			169,000,000		0	0	0	0	102,000,000	88,000,000	20,000,000	20,000,000	0	0	71,000,000	[11]	48,000,000	[11]	3,000,000	3,000,000	1,000,000	2,000,000	8,000,000	8,000,000	0																																																				47,000,000			29,000,000		0	0	21,000,000	22,000,000	0	0	0	0	0	0	8,000,000	[9]	0	8,000,000	0	0	0	0	15,000,000	[7]	7,000,000	[7]	5,000,000	10,000,000	7,000,000	3,000,000																																																						8,000,000
Noncurrent regulatory liabilities	$ 4,115,000,000			$ 3,981,000,000		$ 2,530,000,000	$ 2,397,000,000	$ 1,417,000,000	$ 1,406,000,000	$ 0	$ 0	$ 125,000,000	$ 132,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0									$ 46,000,000																																																												$ 3,337,000,000			$ 3,229,000,000			$ 2,138,000,000	$ 2,037,000,000	$ 1,199,000,000	$ 1,192,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0																																																			$ 560,000,000			$ 538,000,000		$ 392,000,000	$ 360,000,000	$ 0	$ 0	$ 0	$ 0	$ 125,000,000	$ 132,000,000	$ 0	$ 0	$ 0		$ 0		$ 0	$ 0	$ 0	$ 0	$ 43,000,000	$ 46,000,000																																																					$ 218,000,000			$ 214,000,000		$ 0	$ 0	$ 218,000,000	$ 214,000,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0		$ 0		$ 0	$ 0	$ 0	$ 0																																																														$ 43,000,000

[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 and BGE, 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] Pension and other postretirement benefit regulatory assets include a regulatory asset established at the date of the merger related to BGE's portion of the deferred costs associated with legacy Constellation’s pension and other postretirement benefit plans. That BGE-related regulatory asset is being amortized over a period of approximately 12 years, which generally represents the expected average remaining service period of plan participants at the date of the merger

[4] 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.

[5] Represents the regulatory asset recorded at Exelon Corporate representing the fair value of BGE's supply contracts as of the close of the merger date. BGE is allowed full recovery of the costs of its electric and gas supply contracts through approved, regulated rates.

[6] ReIates to integration costs to achieve distribution synergies related to the merger transaction.

[7] Represents the electric and gas distribution costs recoverable from or refundable to customers under BGE’s decoupling mechanism. As of March 31, 2013, includes $5 million of over-recovered electric distribution costs and $10 million of over-recovered gas distribution costs under BGE’s decoupling mechanism. As of December 31, 2012, relates to $5 million of under-recovered electric distribution costs and $7 million of over-recovered gas distribution costs under BGE’s decoupling mechanism.

[8] Relates to under-recovered transmission costs.

[9] Relates to $8 million of over-recovered natural gas supply costs as of March 31, 2013. As of December 31, 2012, includes to $9 million of under-recovered electric supply costs and $19 million of under-recovered natural gas supply costs.

[10] Primarily represents the regulatory liability for revenue subject to refund recorded pursuant to the ICC’s order in the 2007 Rate Case. See Note 3 of Exelon’s 2012 Form 10-K for additional information regarding the 2007 Rate Case.

[11] Includes $39 million related to the over-recovered electric supply costs under the GSA, $26 million related to the over-recovered natural gas costs under the PGC and $6 million related to over-recovered electric transmission costs as of March 31, 2013. As of December 31, 2012, includes $47 million related to the over-recovered electric supply costs under the GSA and $1 million related to the over-recovered natural gas costs under the PGC.