Regulatory Matters (Details) (USD $)																																																																			3 Months Ended	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended																																																															3 Months Ended																																																																							3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011		Aug. 31, 2011	Mar. 31, 2012 Nuclear Decommissioning [Member]	Dec. 31, 2011 Nuclear Decommissioning [Member]	Mar. 31, 2012 Removal Costs [Member]	Dec. 31, 2011 Removal Costs [Member]	Mar. 31, 2012 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2011 Energy Efficiency Demand Response Programs [Member]	Mar. 31, 2012 Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2011 Electric Transmission And Distribution Tax Repairs [Member]	Mar. 31, 2012 Over Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2011 Over Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2012 Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Over Recovered Energy And Transmission Costs [Member]	Mar. 31, 2012 Over-Recovered Universal Service Fund Costs [Member]	Dec. 31, 2011 Over-Recovered Universal Service Fund Costs [Member]	Mar. 31, 2012 Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Over-Recovered AEPS Costs [Member]	Mar. 31, 2012 Customer Rate Credit [Member]	Mar. 31, 2012 Pension and Other Postretirement Benefits [Member]		Dec. 31, 2011 Pension and Other Postretirement Benefits [Member]	Mar. 31, 2012 Deferred Income Taxes [Member]	Dec. 31, 2011 Deferred Income Taxes [Member]	Mar. 31, 2012 AMI Expenses [Member]	Dec. 31, 2011 AMI Expenses [Member]	Mar. 31, 2012 Under Recovered Distribution Service Costs [Member]	Dec. 31, 2011 Under Recovered Distribution Service Costs [Member]	Mar. 31, 2012 Debt Costs [Member]	Dec. 31, 2011 Debt Costs [Member]	Mar. 31, 2012 Fair Value of Acquired Debt [Member]		Mar. 31, 2012 Fair Value of Supply Contracts [Member]		Mar. 31, 2012 Severance [Member]	Dec. 31, 2011 Severance [Member]	Mar. 31, 2012 Asset Retirement Obligations [Member]	Dec. 31, 2011 Asset Retirement Obligations [Member]	Mar. 31, 2012 MGP Remediation Costs [Member]	Dec. 31, 2011 MGP Remediation Costs [Member]	Mar. 31, 2012 RTO Startup Costs [Member]	Dec. 31, 2011 RTO Startup Costs [Member]	Mar. 31, 2012 Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 Under Recovered Universal Service Fund Costs Member [Member]	Dec. 31, 2011 Under Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2012 Financial Swap with Generation [Member]	Dec. 31, 2011 Financial Swap with Generation [Member]	Mar. 31, 2012 Renewable Energy And Associated REC [Member]	Dec. 31, 2011 Renewable Energy And Associated REC [Member]	Mar. 31, 2012 Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2011 Under Recovered Energy And Transmission Costs [Member]	Mar. 31, 2012 DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2011 DSP Program costs [Member]	Mar. 31, 2012 Deferred Storm Costs [Member]	Dec. 31, 2011 Deferred Storm Costs [Member]	Mar. 31, 2012 Electric Generation Related Regulatory Asset [Member]	Dec. 31, 2011 Electric Generation Related Regulatory Asset [Member]	Mar. 31, 2012 Rate Stabilization Deferral [Member]	Dec. 31, 2011 Rate Stabilization Deferral [Member]	Mar. 31, 2012 Energy Efficiency And Demand Response Programs [Member]	Dec. 31, 2011 Energy Efficiency And Demand Response Programs [Member]	Mar. 31, 2012 Other Regulatory Assets [Member]	Dec. 31, 2011 Other Regulatory Assets [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member] One Year From Balance Sheet Date [Member]	Sep. 30, 2008 Commonwealth Edison Co [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Years		Sep. 30, 2011 Commonwealth Edison Co [Member] Years	Sep. 30, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Removal Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Removal Costs [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Customer Rate Credit [Member]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] AMI Expenses [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] AMI Expenses [Member]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Debt Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Debt Costs [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Fair Value of Acquired Debt [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Fair Value of Supply Contracts [Member]		Mar. 31, 2012 Commonwealth Edison Co [Member] Severance [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Severance [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Mar. 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, 2011 Commonwealth Edison Co [Member] Under Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Deferred Storm Costs [Member]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Rate Stabilization Deferral [Member]	Mar. 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]	Mar. 31, 2012 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member] One Year From Balance Sheet Date [Member]	Mar. 31, 2012 PECO Energy Co [Member] SmartMeters		Dec. 31, 2011 PECO Energy Co [Member]		Mar. 31, 2012 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Mar. 31, 2012 PECO Energy Co [Member] Removal Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Removal Costs [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]		Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Mar. 31, 2012 PECO Energy Co [Member] Customer Rate Credit [Member]	Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2011 PECO Energy Co [Member] Deferred Income Taxes [Member]	Mar. 31, 2012 PECO Energy Co [Member] AMI Expenses [Member]	Dec. 31, 2011 PECO Energy Co [Member] AMI Expenses [Member]	Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] Debt Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Debt Costs [Member]	Mar. 31, 2012 PECO Energy Co [Member] Fair Value of Acquired Debt [Member]		Mar. 31, 2012 PECO Energy Co [Member] Fair Value of Supply Contracts [Member]		Mar. 31, 2012 PECO Energy Co [Member] Severance [Member]	Dec. 31, 2011 PECO Energy Co [Member] Severance [Member]	Mar. 31, 2012 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2011 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Mar. 31, 2012 PECO Energy Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] MGP Remediation Costs [Member]	Mar. 31, 2012 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] RTO Startup Costs [Member]	Mar. 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, 2011 PECO Energy Co [Member] Under Recovered Uncollectible Accounts Expense [Member]	Mar. 31, 2012 PECO Energy Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2011 PECO Energy Co [Member] Financial Swap with Generation [Member]	Mar. 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]	Mar. 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]		Mar. 31, 2012 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2011 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 31, 2012 PECO Energy Co [Member] DSP Program costs [Member]	Mar. 31, 2012 PECO Energy Co [Member] Deferred Storm Costs [Member]	Dec. 31, 2011 PECO Energy Co [Member] Deferred Storm Costs [Member]	Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Dec. 31, 2011 PECO Energy Co [Member] Rate Stabilization Deferral [Member]	Mar. 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]	Mar. 31, 2012 PECO Energy Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2011 PECO Energy Co [Member] Other Regulatory Assets [Member]	Mar. 31, 2012 PECO Energy Co [Member] More Than One And Within Two Years From Balance Sheet Date [Member] AlternativeEnergyCredits	Mar. 31, 2012 PECO Energy Co [Member] More Than Three And Within Four Years From Balance Sheet Date [Member] AlternativeEnergyCredits	Mar. 31, 2012 PECO Energy Co [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member] AlternativeEnergyCredits	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]		Dec. 31, 2011 Baltimore Gas and Electric Company [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Nuclear Decommissioning [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Removal Costs [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Customer Rate Credit [Member]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] AMI Expenses [Member]	Mar. 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]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Debt Costs [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Fair Value of Acquired Debt [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Fair Value of Supply Contracts [Member]		Mar. 31, 2012 Baltimore Gas and Electric Company [Member] Severance [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] Severance [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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, 2011 Baltimore Gas and Electric Company [Member] Under Recovered Uncollectible Accounts Expense [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member] DSP Program Electric Procurement Contracts [Member]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]	Mar. 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]
Purchase Of Receivables [Line Items]
POR gross receivables	$ 146,000,000		$ 68,000,000																																																																		$ 20,000,000				$ 16,000,000																																																																$ 57,000,000		$ 52,000,000																																																																							$ 69,000,000		$ 61,000,000
POR Allowance for uncollectible accounts	13,000,000	[1]	5,000,000	[1]																																																																	3,000,000	[1]			0	[1]																																																															6,000,000	[1]	5,000,000	[1]																																																																						4,000,000	[1]	3,000,000	[1]
POR net receivables	133,000,000		63,000,000																																																																		17,000,000				16,000,000																																																																51,000,000		47,000,000																																																																							65,000,000		58,000,000
Distribution Rate Case [Abstract]
Rate of return on common equity electric distribution																																																																				10.30%
Intervenor potential refund submitted in testimony					37,000,000
Increase in electric delivery service revenue resulting from rate case settlement																																																																																																																																									225,000,000
Increase in gas delivery service revenue resulting from rate case settlement																																																																																																																																									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
Illinois Legislation for Recovery of Uncollectible Accounts [Abstract]
Under-collected uncollectible accounts regulatory asset																																																																								70,000,000
Smart Meter and Smart Grid Investments [Abstract]
Estimated number of smart meters to be installed																																																																																																																																									1,600,000
Smart grid investment grant amount																																																																																																																																									200,000,000
Reimbursable DOE Smart Grid Investment Grant expenditures																																																																																																																																									28,000,000
Reimbursements received from the DOE																																																																																																																																									87,000,000
Total Projected smart meter smart grid spend																																																																																																																																																																																																																	650,000,000
Energy Efficiency Program [Abstract]
EE 2011 Compliance Target																																																																																																																																									0.01%
Advanced metering infrastructure pilot program [Abstract]
Collections Under Rider Amp																																																																									24,000,000
Alternative Energy Portfolio Standards [Abstract]
Minimum percentage Tier I alternative energy resources																																																																																																																																									0.035%
Maximum percentage Tier I alternative energy resources																																																																																																																																									0.08%
Minimum percentage Tier II alternative energy resources																																																																																																																																									0.062%
Maximum percentage Tier II alternative energy resources																																																																																																																																									0.10%
Total alternative energy credits purchased annually																																																																																																																																																																																																																0
Solar tier 1 alternative energy credits purchased annually																																																																																																																																																																																																																	0
Tier II AECs Purchased																																																																																																																																																																																																															340,000
Proposed Legislation to Modernize Electric Utility Infrastructure and to Update Illinois Ratemaking Process
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
Time period for AMI Deployment																																																																							10
Planned capital spend by a utility under state enacted legislation																																																																					233,000,000
Customer Assistance Program Time Period																																																																					5
Over or Under recovered distribution service costs																																																																					118,000,000				84,000,000
Revenue reduction issued by ALJ in proposed order																																																																					146,000,000
Revenue reduction stated in the Utilities final position in the tariff proceeding.																																																																					59,000,000
Portion of distribution regulatory asset																																																																			61,000,000		57,000,000
Change to the asset or liability related to prior year expenses																																																																																																																																								19,000,000
Natural Gas Supplier Tariff [Abstract]
Natural gas supplier tariff collateral																																																																																																																																									14,000,000
Regulatory Asset [Line Items]
Noncurrent regulatory assets	6,168,000,000		4,518,000,000																				3,512,000,000	[2]	2,794,000,000	1,243,000,000	1,176,000,000	46,000,000	28,000,000	99,000,000	70,000,000	78,000,000	81,000,000	253,000,000	[3]	89,000,000	[4]	44,000,000	38,000,000	76,000,000	74,000,000	124,000,000	129,000,000	3,000,000	4,000,000	0	0	0	0	0	125,000,000	97,000,000	0	0	2,000,000	2,000,000	8,000,000	0	52,000,000	0	282,000,000	0	100,000,000	0	32,000,000	25,000,000			644,000,000				699,000,000																			0	[2]	0	64,000,000	66,000,000	6,000,000	6,000,000	99,000,000	70,000,000	70,000,000	73,000,000	0	[3]	0	[4]	31,000,000	38,000,000	52,000,000	50,000,000	85,000,000	91,000,000	3,000,000	4,000,000	0	0	0	92,000,000	191,000,000	125,000,000	97,000,000	0	0	0	0	0	0	0	0	0	0	0	0	17,000,000	13,000,000		1,217,000,000		1,216,000,000																					0	[2]	0	1,115,000,000	1,110,000,000	22,000,000	22,000,000	0	0	8,000,000	8,000,000	0	[3]	0	[4]	0	0	24,000,000	24,000,000	37,000,000	38,000,000	0	0	0	0	0	0	0	0	0	0		0		2,000,000	2,000,000		0	0	0	0	0	0	0	0	9,000,000	12,000,000				553,000,000		550,000,000																			0	[2]	0	64,000,000	64,000,000	18,000,000	15,000,000	0	0	10,000,000	10,000,000	0	[3]	0	[4]	13,000,000	1,000,000	0	0	2,000,000	2,000,000	0	0	0	0	0	0	0	0	0	0	0	0	0	8,000,000	9,000,000	52,000,000	56,000,000	282,000,000	295,000,000	100,000,000	95,000,000	4,000,000	3,000,000
Current regulatory assets	846,000,000		390,000,000																				265,000,000	[2]	204,000,000	12,000,000	5,000,000	2,000,000	2,000,000	19,000,000	14,000,000	15,000,000	18,000,000	41,000,000	[3]	117,000,000	[4]	28,000,000	25,000,000	0	0	31,000,000	30,000,000	3,000,000	3,000,000	5,000,000	3,000,000	0	0	0	16,000,000	9,000,000	139,000,000	57,000,000	3,000,000	3,000,000	3,000,000	0	16,000,000	0	63,000,000	0	29,000,000	0	39,000,000	17,000,000			793,000,000				657,000,000																			0	[2]	0	5,000,000	5,000,000	2,000,000	2,000,000	19,000,000	14,000,000	12,000,000	15,000,000	0	[3]	0	[4]	25,000,000	25,000,000	0	0	24,000,000	24,000,000	3,000,000	3,000,000	0	0	0	590,000,000	503,000,000	16,000,000	9,000,000	85,000,000	48,000,000	0	0	0	0	0	0	0	0	0	0	12,000,000	9,000,000		48,000,000		39,000,000																					5,000,000	[2]	7,000,000	0	0	0	0	0	0	3,000,000	3,000,000	0	[3]	0	[4]	0	0	0	0	6,000,000	6,000,000	0	0	5,000,000	3,000,000	0	0	0	0	0	9,000,000	[5]	9,000,000	[5]		3,000,000	3,000,000	0	0	0	0	0	0	0	0	17,000,000	8,000,000				174,000,000		174,000,000																			2,000,000	[2]	3,000,000	7,000,000	7,000,000	0	0	0	0	2,000,000	2,000,000	0	[3]	0	[4]	3,000,000	0	0	0	1,000,000	1,000,000	0	0	0	0	0	0	0	0	0	45,000,000	50,000,000	0	0	3,000,000	3,000,000	16,000,000	16,000,000	63,000,000	63,000,000	29,000,000	29,000,000	3,000,000	0
Regulatory Asset Liability Table Footnote Data [Abstract]
Approved Recovery Of Restructuring Costs																																																																							13,000,000
Regulatory Liabilities [Line Items]
Regulatory Liability Current	335,000,000		197,000,000			0	0	86,000,000	61,000,000	42,000,000	49,000,000	20,000,000	19,000,000	10,000,000	15,000,000	55,000,000	42,000,000	3,000,000	3,000,000	6,000,000	8,000,000	113,000,000																																															127,000,000				137,000,000		0	0	64,000,000	61,000,000	42,000,000	49,000,000	0	0	10,000,000	15,000,000	11,000,000	12,000,000	0	0	0	0	0																																														73,000,000		60,000,000		0	0	0	0	0	0	20,000,000	19,000,000	0	0	44,000,000	[6]	30,000,000	[6]	3,000,000	3,000,000	6,000,000	8,000,000	0																																																			135,000,000		18,000,000		0	0	22,000,000	18,000,000	0	0	0	0	0	0	0	0	0	0	0	0	113,000,000
Noncurrent regulatory liabilities	4,050,000,000		3,627,000,000			2,430,000,000	2,222,000,000	1,396,000,000	1,185,000,000	79,000,000	69,000,000	145,000,000	151,000,000	0	0	0	0	0	0	0	0	0																																															3,208,000,000				3,042,000,000		2,017,000,000	1,857,000,000	1,191,000,000	1,185,000,000	0	0	0	0	0	0	0	0	0	0	0	0	0																																														637,000,000		585,000,000		413,000,000	365,000,000	0	0	79,000,000	69,000,000	145,000,000	151,000,000	0	0	0		0		0	0	0	0	0																																																			205,000,000		200,000,000		0	0	205,000,000	200,000,000	0	0	0	0	0	0	0	0	0	0	0	0	0
Regulatory Liabilities Table Footnote Data [Abstract]
Purchased Natural Gas Cost Over-Recovery																																																																																																																																									18,000,000		5,000,000
Electric Supply Cost Over-Recovery																																																																																																																																									$ 26,000,000		$ 25,000,000

[1] 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.

[2] As of March 31, 2012, the pensions and other postretirement benefits line now includes a regulatory asset established at the date of the merger related to the recognition of BGE’s share of the underfunded status of the defined benefit postretirement plan as a liability on Exelon’s balance sheet. The regulatory asset is amortized in proportion to the recognition of prior service costs (gains), transition obligations, and actuarial losses attributable to BGE’s share of the postretirement plans determined by the cost recognition provisions of the authoritative guidance for pensions and postretirement benefitsaccordance with the authoritative guidance for pensions and postretirement benefits over a period of approximately 12 years. BGE is currently recovering these costs through base rates. BGE is not earning a return on the recovery of these costs in base rates.

[3] 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.

[4] 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.

[5] Relates to the under-recovered transmission costs.

[6] Includes $18 million and $5 million related to the over-recovered natural gas costs under the PGC and $26 million and $25 million related to the over-recovered electric supply costs under the GSA as of March 31, 2012 and December 31, 2011, respectively.