Regulatory Matters (Details) (USD $)	3 Months Ended		9 Months Ended				1 Months Ended	3 Months Ended			9 Months Ended			12 Months Ended																																													3 Months Ended		9 Months Ended				9 Months Ended																																														9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Aug. 31, 2011	Dec. 31, 2010	Sep. 30, 2008 Commonwealth Edison Co [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2010 Commonwealth Edison Co [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member] SmartMeters BasisPoints MGPSites	Sep. 30, 2010 Commonwealth Edison Co [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member]	Aug. 31, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] AMI Expenses [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] AMI Expenses [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Pension and Other Postretirement Benefits [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Deferred Income Taxes [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Debt Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Debt Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Severance [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Severance [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Asset Retirement Obligations [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] MGP Remediation Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] RTO Startup Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Under Recovered Uncollectible Accounts Expense [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Financial Swap with Generation [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Derivative Liability [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] DSP Program Electric Procurement Contracts [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Other Regulatory Assets [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Under Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] DSP Program costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] DSP Program costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Nuclear Decommissioning [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Removal Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Removal Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Real Estate Tax [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Real Estate Tax [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Regulatory Liabilities Other [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Over Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Derivative Asset [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Over-Recovered AEPS Costs [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Sep. 30, 2011 PECO Energy Co [Member] SmartMeters BasisPoints MGPSites	Sep. 30, 2010 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member] SmartMeters BasisPoints MGPSites	Sep. 30, 2010 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]	Dec. 16, 2010 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member] More Than One And Within Two Years From Balance Sheet Date [Member] AlternativeEnergyCredits	Sep. 30, 2011 PECO Energy Co [Member] More Than Three And Within Four Years From Balance Sheet Date [Member] AlternativeEnergyCredits	Sep. 30, 2011 PECO Energy Co [Member] More Than Five Years From Balance Sheet Date And Thereafter [Member] AlternativeEnergyCredits	Sep. 30, 2011 PECO Energy Co [Member] AMI Expenses [Member]	Dec. 31, 2010 PECO Energy Co [Member] AMI Expenses [Member]	Sep. 30, 2011 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]	Dec. 31, 2010 PECO Energy Co [Member] Pension and Other Postretirement Benefits [Member]	Sep. 30, 2011 PECO Energy Co [Member] Deferred Income Taxes [Member]	Dec. 31, 2010 PECO Energy Co [Member] Deferred Income Taxes [Member]	Sep. 30, 2011 PECO Energy Co [Member] Debt Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Debt Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Severance [Member]	Dec. 31, 2010 PECO Energy Co [Member] Severance [Member]	Sep. 30, 2011 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Dec. 31, 2010 PECO Energy Co [Member] Asset Retirement Obligations [Member]	Sep. 30, 2011 PECO Energy Co [Member] MGP Remediation Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] MGP Remediation Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] RTO Startup Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Under Recovered Uncollectible Accounts Expense [Member]	Sep. 30, 2011 PECO Energy Co [Member] Financial Swap with Generation [Member]	Dec. 31, 2010 PECO Energy Co [Member] Financial Swap with Generation [Member]	Sep. 30, 2011 PECO Energy Co [Member] Derivative Liability [Member]	Sep. 30, 2011 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2010 PECO Energy Co [Member] DSP Program Electric Procurement Contracts [Member]	Sep. 30, 2011 PECO Energy Co [Member] Other Regulatory Assets [Member]	Dec. 31, 2010 PECO Energy Co [Member] Other Regulatory Assets [Member]	Sep. 30, 2011 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Under Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] DSP Program costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] DSP Program costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Dec. 31, 2010 PECO Energy Co [Member] Nuclear Decommissioning [Member]	Sep. 30, 2011 PECO Energy Co [Member] Removal Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Real Estate Tax [Member]	Dec. 31, 2010 PECO Energy Co [Member] Real Estate Tax [Member]	Sep. 30, 2011 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Energy Efficiency Demand Response Programs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Electric Transmission And Distribution Tax Repairs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Regulatory Liabilities Other [Member]	Sep. 30, 2011 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2010 PECO Energy Co [Member] Over Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Derivative Asset [Member]	Sep. 30, 2011 PECO Energy Co [Member] Over-Recovered Universal Service Fund Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Over-Recovered AEPS Costs [Member]	Sep. 30, 2011 PECO Energy Co [Member] Over Recovered Uncollectible Accounts Expense [Member]	Sep. 30, 2011 Exelon Corporate [Member]	Sep. 30, 2011 Exelon Corporate [Member] Financial Swap with Generation [Member]	Sep. 30, 2011 Severance [Member]	Dec. 31, 2010 Severance [Member]	Sep. 30, 2011 Pension and Other Postretirement Benefits [Member]	Dec. 31, 2010 Pension and Other Postretirement Benefits [Member]	Sep. 30, 2011 AMI Expenses [Member]	Dec. 31, 2010 AMI Expenses [Member]	Sep. 30, 2011 Deferred Income Taxes [Member]	Dec. 31, 2010 Deferred Income Taxes [Member]	Sep. 30, 2011 Debt Costs [Member]	Dec. 31, 2010 Debt Costs [Member]	Sep. 30, 2011 Asset Retirement Obligations [Member]	Dec. 31, 2010 Asset Retirement Obligations [Member]	Sep. 30, 2011 MGP Remediation Costs [Member]	Dec. 31, 2010 MGP Remediation Costs [Member]	Sep. 30, 2011 RTO Startup Costs [Member]	Dec. 31, 2010 RTO Startup Costs [Member]	Sep. 30, 2011 Under Recovered Uncollectible Accounts Expense [Member]	Dec. 31, 2010 Under Recovered Uncollectible Accounts Expense [Member]	Sep. 30, 2011 Financial Swap with Generation [Member]	Dec. 31, 2010 Financial Swap with Generation [Member]	Sep. 30, 2011 Derivative Liability [Member]	Sep. 30, 2011 DSP Program Electric Procurement Contracts [Member]	Dec. 31, 2010 DSP Program Electric Procurement Contracts [Member]	Sep. 30, 2011 Other Regulatory Assets [Member]	Dec. 31, 2010 Other Regulatory Assets [Member]	Sep. 30, 2011 Under Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 Nuclear Decommissioning [Member]	Dec. 31, 2010 Nuclear Decommissioning [Member]	Sep. 30, 2011 Removal Costs [Member]	Dec. 31, 2010 Removal Costs [Member]	Sep. 30, 2011 Real Estate Tax [Member]	Dec. 31, 2010 Real Estate Tax [Member]	Sep. 30, 2011 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2010 Energy Efficiency Demand Response Programs [Member]	Dec. 31, 2010 Regulatory Liabilities Other [Member]	Sep. 30, 2011 Over Recovered Energy And Transmission Costs [Member]	Dec. 31, 2010 Over Recovered Energy And Transmission Costs [Member]	Sep. 30, 2011 Derivative Asset [Member]	Sep. 30, 2011 Over-Recovered Universal Service Fund Costs [Member]	Sep. 30, 2011 Over-Recovered AEPS Costs [Member]	Sep. 30, 2011 Over Recovered Uncollectible Accounts Expense [Member]
Operating And Maintenance For Regulatory Required Programs [Line Items]
Energy efficiency and demand response programs	$ 52,000,000	$ 35,000,000	$ 122,000,000	$ 93,000,000				$ 41,000,000	$ 21,000,000	[1]	$ 80,000,000	$ 59,000,000	[1]																																														$ 11,000,000	$ 14,000,000	$ 42,000,000	$ 34,000,000
Advanced metering infrastructure pilot program	3,000,000		7,000,000					0			0																																																3,000,000		7,000,000
Purchased power administrative costs	3,000,000	1,000,000	7,000,000	3,000,000				2,000,000	1,000,000		4,000,000	3,000,000																																															1,000,000		3,000,000	0
Consumer education program	1,000,000	1,000,000	2,000,000	2,000,000				0	0		0	0																																															1,000,000	1,000,000	2,000,000	2,000,000
Total operating and maintenance for regulatory required programs	59,000,000	37,000,000	138,000,000	98,000,000				43,000,000	22,000,000		84,000,000	62,000,000																																															16,000,000	15,000,000	54,000,000	36,000,000
Distribution Rate Case [Abstract]
One-time benefit to reverse prior charges and record regulatory assets								40,000,000			40,000,000
Requested increase in electric revenues														396,000,000
Adjustment to Requested increase in electric revenues								85,000,000			85,000,000
Requested rate of return on common equity											11.50%
Rate of return on common equity electric distribution							10.30%				10.50%
Maximum potential refund submitted in testimony by registrant															30,000,000
Intervenor potential refund submitted in testimony					37,000,000
Expected increase in electric delivery rates											0.05%
Increase in electric delivery service revenue resulting from rate case settlement								143,000,000			143,000,000																																																					225,000,000
Increase in gas delivery service revenue resulting from rate case settlement																																																																20,000,000
ComEd's proposed increase to net distribution revenue requirement related to uncollectable account expense											22,000,000
Severance noncurrent regulatory asset								68,000,000			68,000,000
Reply brief requested increase in electric revenues.								343,000,000			343,000,000
Proposed increase in electric revenues								152,000,000			152,000,000
Proposed rate of return on common equity											10.50%
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
Chicago areas smart meters installed											131,000
Chicago area smart meters, approved for installation											131,000
Illinois Procurement Proceedings [Abstract]
Revenue subject to refund reversal											17,000,000
Illinois Legislation for Recovery of Uncollectible Accounts [Abstract]
Under-collected uncollectible accounts regulatory asset												70,000,000
One-time operating and maintenance expense charge												10,000,000
Annual Transmission Formula Rate Update [Abstract]
Gross transmission revenue requirement											438,000,000	416,000,000
Transmission revenue true up											16,000,000			16,000,000																																														422,000,000
Net transmission revenue requirement											422,000,000
PJM Minimum Offer Price Rule [Abstract]
Subsidized Plant Minimum Bid																																																																																																															0.90%
Smart Meter and Smart Grid Investments [Abstract]
Estimated number of smart meters to be installed																																																											1,600,000		1,600,000
Smart grid investment grant amount																																																											200,000,000		200,000,000
Reimbursable DOE Smart Grid Investment Grant expenditures																																																											16,000,000		16,000,000
Reimbursements received from the DOE																																																											52,000,000		52,000,000
Total Projected smart meter smart grid spend																																																																			650,000,000
Energy Efficiency Program [Abstract]
EE 2011 Compliance Target																																																													1.00%
Alternative Energy Portfolio Standards [Abstract]
Minimum percentage Tier I alternative energy resources																																																													3.50%
Maximum percentage Tier I alternative energy resources																																																													8.00%
Minimum percentage Tier II alternative energy resources																																																													6.20%
Maximum percentage Tier II alternative energy resources																																																													10.00%
Total alternative energy credits purchased annually																																																																		0
Solar tier 1 alternative energy credits purchased annually																																																																			0
Tier II AECs Purchased																																																																	340,000
Authorized Return On Rate Base [Abstract]
Weighted Average Debt And Equity Return Electric Distribution											9.10%
Weighted Average Debt And Equity Return											0.091%	0.0927%
Rate Of Return On Common Equity											11.50%																																																		11.50%
Common Equity Component Cap											0.55%																																																		55.00%
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
Potential Additional investment to modernize system and implement smart grid technology											3,000,000
POR Receivables																																																											53,000,000		53,000,000
PY POR Receivables																																																															3,000,000
Regulatory Asset [Line Items]
Noncurrent regulatory assets	4,381,000,000		4,381,000,000			4,140,000,000		733,000,000			733,000,000			947,000,000		9,000,000	0	0	0	70,000,000	23,000,000	93,000,000	108,000,000	69,000,000	74,000,000	50,000,000	61,000,000	115,000,000	110,000,000	8,000,000	10,000,000	14,000,000	247,000,000	525,000,000	48,000,000			24,000,000	22,000,000			0	0																1,233,000,000		1,233,000,000		968,000,000					22,000,000	17,000,000	8,000,000	13,000,000	1,091,000,000	829,000,000	12,000,000	15,000,000	0	0	24,000,000	25,000,000	46,000,000	39,000,000	0	0	0	0	0	0			24,000,000	23,000,000			6,000,000	7,000,000																	0	69,000,000	74,000,000	2,671,000,000	2,763,000,000	31,000,000	17,000,000	1,161,000,000	852,000,000	105,000,000	123,000,000	74,000,000	86,000,000	161,000,000	149,000,000	8,000,000	10,000,000	14,000,000			0	48,000,000	6,000,000	7,000,000	47,000,000	45,000,000
Current regulatory assets	31,000,000		31,000,000			10,000,000		441,000,000			441,000,000			456,000,000																			415,000,000	450,000,000	2,000,000	0	0			24,000,000	6,000,000																		7,000,000		7,000,000		9,000,000																						0	0	0	3,000,000	9,000,000			4,000,000	0																																					6,000,000	0	0	2,000,000	1,000,000	4,000,000			28,000,000
Total regulatory assets	4,412,000,000		4,412,000,000			4,150,000,000		1,174,000,000			1,174,000,000			1,403,000,000																																													1,240,000,000		1,240,000,000		977,000,000
Regulatory Asset Liability Table Footnote Data [Abstract]
Electric Supply Cost Under-Recovery	0		0
Transmission Cost Under-Recovery	0		0
Approved Recovery Of Restructuring Costs								13,000,000			13,000,000
Regulatory Liabilities [Line Items]
Noncurrent regulatory liabilities	3,601,000,000		3,601,000,000			3,555,000,000		3,038,000,000			3,038,000,000			3,137,000,000																														1,748,000,000	1,892,000,000	1,239,000,000	1,211,000,000	0	0	46,000,000	31,000,000	(1,000,000)			4,000,000			5,000,000	563,000,000		563,000,000		418,000,000																																	329,000,000	375,000,000	0	1,000,000	4,000,000	62,000,000	38,000,000	171,000,000	1,000,000			0			0	171,000,000																												2,077,000,000	2,267,000,000	1,239,000,000	1,211,000,000	1,000,000	4,000,000	108,000,000	69,000,000	0			4,000,000			5,000,000
Regulatory liabilities	60,000,000		60,000,000			44,000,000		17,000,000			17,000,000			19,000,000																																							17,000,000	19,000,000		0	0		43,000,000		43,000,000		25,000,000																																										33,000,000	25,000,000		3,000,000	7,000,000																																							50,000,000	44,000,000		3,000,000	7,000,000
Total regulatory liabilities	3,661,000,000		3,661,000,000			3,599,000,000		3,055,000,000			3,055,000,000			3,156,000,000																																													606,000,000		606,000,000		443,000,000
Regulatory Liabilities Table Footnote Data [Abstract]
Purchased Natural Gas Cost Over-Recovery																																																											(14,000,000)		(14,000,000)
Electric Supply Cost Over-Recovery	$ (19,000,000)		$ (19,000,000)

[1] As a result of the Illinois Settlement Legislation, Illinois utilities are required to provide energy efficiency and demand response programs.