Property, Plant and Equipment (Details) (USD $)						12 Months Ended		12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended						12 Months Ended									12 Months Ended				12 Months Ended						12 Months Ended						12 Months Ended				12 Months Ended						12 Months Ended		12 Months Ended		12 Months Ended				12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Mar. 31, 2009	Dec. 31, 2011 Electric Transmission And Distribution [Member] Years	Dec. 31, 2010 Electric Transmission And Distribution [Member]	Dec. 31, 2011 Electric Generation Equipment [Member] Years		Dec. 31, 2010 Electric Generation Equipment [Member]		Dec. 31, 2011 Gas Distribution Equipment [Member] Years	Dec. 31, 2010 Gas Distribution Equipment [Member]	Dec. 31, 2011 Common Electric And Gas T And D Equipment [Member] Years	Dec. 31, 2010 Common Electric And Gas T And D Equipment [Member]	Dec. 31, 2011 Nuclear Fuel [Member] Years		Dec. 31, 2010 Nuclear Fuel [Member]		Dec. 31, 2011 Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2010 Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2011 Other Capitalized Property Plant And Equipment [Member] Years		Dec. 31, 2010 Other Capitalized Property Plant And Equipment [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]		Mar. 31, 2009 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Electric Generation Equipment [Member] Years		Dec. 31, 2010 Exelon Generation Co L L C [Member] Electric Generation Equipment [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Nuclear Fuel [Member] Years		Dec. 31, 2010 Exelon Generation Co L L C [Member] Nuclear Fuel [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Other Capitalized Property Plant And Equipment [Member] Years		Dec. 31, 2010 Exelon Generation Co L L C [Member] Other Capitalized Property Plant And Equipment [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Electric Transmission And Distribution [Member] Years	Dec. 31, 2010 Commonwealth Edison Co [Member] Electric Transmission And Distribution [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Other Capitalized Property Plant And Equipment [Member] Years		Dec. 31, 2010 Commonwealth Edison Co [Member] Other Capitalized Property Plant And Equipment [Member]		Dec. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]	Dec. 31, 2011 PECO Energy Co [Member] Electric Transmission And Distribution [Member] Years	Dec. 31, 2010 PECO Energy Co [Member] Electric Transmission And Distribution [Member]	Dec. 31, 2011 PECO Energy Co [Member] Gas Distribution Equipment [Member] Years	Dec. 31, 2010 PECO Energy Co [Member] Gas Distribution Equipment [Member]	Dec. 31, 2011 PECO Energy Co [Member] Common Electric And Gas T And D Equipment [Member] Years	Dec. 31, 2010 PECO Energy Co [Member] Common Electric And Gas T And D Equipment [Member]	Dec. 31, 2011 PECO Energy Co [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2010 PECO Energy Co [Member] Public Utilities Property Plant And Equipment Construction Work In Progress [Member]	Dec. 31, 2011 PECO Energy Co [Member] Other Capitalized Property Plant And Equipment [Member] Years		Dec. 31, 2010 PECO Energy Co [Member] Other Capitalized Property Plant And Equipment [Member]		Dec. 31, 2011 Electric Transmission And Distribution [Member]	Dec. 31, 2010 Electric Transmission And Distribution [Member]	Dec. 31, 2009 Electric Transmission And Distribution [Member]	Dec. 31, 2011 Electric Transmission And Distribution [Member] Commonwealth Edison Co [Member]	Dec. 31, 2010 Electric Transmission And Distribution [Member] Commonwealth Edison Co [Member]	Dec. 31, 2009 Electric Transmission And Distribution [Member] Commonwealth Edison Co [Member]	Dec. 31, 2011 Electric Transmission And Distribution [Member] PECO Energy Co [Member]	Dec. 31, 2010 Electric Transmission And Distribution [Member] PECO Energy Co [Member]	Dec. 31, 2009 Electric Transmission And Distribution [Member] PECO Energy Co [Member]	Dec. 31, 2011 Electric Generation Equipment [Member]	Dec. 31, 2010 Electric Generation Equipment [Member]	Dec. 31, 2009 Electric Generation Equipment [Member]	Dec. 31, 2011 Electric Generation Equipment [Member] Exelon Generation Co L L C [Member]	Dec. 31, 2010 Electric Generation Equipment [Member] Exelon Generation Co L L C [Member]	Dec. 31, 2009 Electric Generation Equipment [Member] Exelon Generation Co L L C [Member]	Dec. 31, 2011 Gas Distribution Equipment [Member]	Dec. 31, 2010 Gas Distribution Equipment [Member]	Dec. 31, 2009 Gas Distribution Equipment [Member]	Dec. 31, 2011 Gas Distribution Equipment [Member] PECO Energy Co [Member]	Dec. 31, 2010 Gas Distribution Equipment [Member] PECO Energy Co [Member]	Dec. 31, 2009 Gas Distribution Equipment [Member] PECO Energy Co [Member]	Dec. 31, 2011 Common Electric And Gas T And D Equipment [Member]	Dec. 31, 2010 Common Electric And Gas T And D Equipment [Member]	Dec. 31, 2009 Common Electric And Gas T And D Equipment [Member]	Dec. 31, 2011 Common Electric And Gas T And D Equipment [Member] PECO Energy Co [Member]	Dec. 31, 2010 Common Electric And Gas T And D Equipment [Member] PECO Energy Co [Member]	Dec. 31, 2009 Common Electric And Gas T And D Equipment [Member] PECO Energy Co [Member]
Property Plant And Equipment Average Service Life Percentage By Asset Category [Line Items]
Annual depreciation rate																																																																					2.59%	2.53%	2.43%	2.67%	2.64%	2.57%	2.33%	2.17%	1.97%	3.12%	2.86%	2.28%	3.12%	2.86%	2.28%	1.73%	1.75%	1.75%	1.73%	1.75%	1.75%	8.05%	7.25%	6.41%	8.05%	7.25%	6.41%
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 43,529,000,000		$ 40,005,000,000			$ 21,716,000,000	$ 20,389,000,000	$ 13,682,000,000	[1]	$ 11,914,000,000	[1]	$ 1,793,000,000	$ 1,732,000,000	$ 564,000,000	$ 534,000,000	$ 4,225,000,000	[2]	$ 3,725,000,000	[2]	$ 1,110,000,000	$ 1,290,000,000	$ 439,000,000	[3]	$ 421,000,000	[3]	$ 18,788,000,000		$ 16,542,000,000			$ 13,682,000,000	[1]	$ 11,914,000,000	[1]	$ 4,225,000,000	[2]	$ 3,725,000,000	[2]	$ 827,000,000	$ 849,000,000	$ 54,000,000	[4]	$ 54,000,000	[4]	$ 15,871,000,000	$ 15,006,000,000	$ 15,637,000,000	$ 14,752,000,000	$ 187,000,000	$ 207,000,000	$ 47,000,000	[5]	$ 47,000,000	[5]	$ 8,536,000,000	$ 8,151,000,000	$ 6,079,000,000	$ 5,637,000,000	$ 1,793,000,000	$ 1,732,000,000	$ 564,000,000	$ 534,000,000	$ 83,000,000	$ 231,000,000	$ 17,000,000	[5]	$ 17,000,000	[5]
Less: accumulated depreciation	(10,959,000,000)	[6]	(10,064,000,000)	[6]																						(5,313,000,000)	[7]	(4,880,000,000)	[7]																(2,750,000,000)	(2,428,000,000)									(2,662,000,000)	(2,531,000,000)
Property, plant and equipment, net	32,570,000,000		29,941,000,000																							13,475,000,000		11,662,000,000																	13,121,000,000	12,578,000,000									5,874,000,000	5,620,000,000
Average Service Life (years) Min.						5		1				5		5		1						4									1				1						4						5				50						5		5		5				50
Average Service Life (years) Max.						75		54				70		50		8						50									54				8						22						75				50						65		70		50				50
Property Plant And Equipment Footnotes [Abstract]
Nuclear fuel - work in progress	674,000,000		651,000,000																							674,000,000		651
Buildings under capital lease	23,000,000		26,000,000																							23,000,000		26,000,000
Original cost basis for buildings	53,000,000																									53,000,000
Accumulated depreciation for buildings	30,000,000		27,000,000																									27,000,000
Accumulated amortization of nuclear fuel	1,784,000,000		1,592,000,000																							1,784,000,000		1,592,000,000
Impairment Of Fossil Plants [Abstract]
Fossil plants impairment charge					$ 223,000,000																									$ 223,000,000

[1] Includes assets acquired through acquisitions. See Note 3 - Acquisition for additional information.

[2] Includes nuclear fuel that is in the fabrication and installation phase of $674 million and $651 million at December 31, 2011 and 2010, respectively.

[3] Includes Generation's buildings under capital lease with a net carrying value of $23 million and $26 million at December 31, 2011 and 2010, respectively. The original cost basis of the buildings was $53 million and total accumulated amortization was $30 million and $27 million as of December 31, 2011 and 2010, respectively. Also includes unregulated property at ComEd and PECO.

[4] Includes buildings under capital lease with a net carrying value of $23 million and $26 million at December 31, 2011 and 2010, respectively. The original cost basis of the buildings was $53 million and total accumulated amortization was $30 million and $27 million as of December 31, 2011 and 2010, respectively.

[5] Represents unregulated property.

[6] Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $1,784 million and $1,592 million as of December 31, 2011 and 2010, respectively.

[7] Includes accumulated amortization of nuclear fuel in the reactor core of $1,784 million and $1,592 million as of December 31, 2011 and 2010, respectively.