Corporate Restructuring and Plant Retirements (Details) (USD $)	6 Months Ended	12 Months Ended								25 Months Ended	12 Months Ended										6 Months Ended	12 Months Ended												6 Months Ended	12 Months Ended
	Jun. 30, 2009 EmployeePositions	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2009 Severance [Member]	Dec. 31, 2009 Contractual Termination Benefits [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] EmployeePositions	Dec. 31, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2009 Exelon Generation Co L L C [Member] GeneratingUnits	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Expected Severance Costs [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Expected Severance Costs [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Expected Inventory Write Down Costs [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Expected Plant Shut Down Costs [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Eddystone Generating Station [Member]	Dec. 31, 2009 Exelon Generation Co L L C [Member] Corporate Restructuring [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Plant Retirements [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Plant Retirements [Member]	Dec. 31, 2009 Exelon Generation Co L L C [Member] Plant Retirements [Member]	Jun. 30, 2009 Commonwealth Edison Co [Member] EmployeePositions	Dec. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2009 Commonwealth Edison Co [Member]	Dec. 31, 2009 Commonwealth Edison Co [Member] Corporate Restructuring [Member]		Dec. 31, 2010 PECO Energy Co [Member]	Dec. 31, 2009 PECO Energy Co [Member]	Dec. 31, 2009 PECO Energy Co [Member] Corporate Restructuring [Member]		Dec. 31, 2011 Other Segment [Member]	Dec. 31, 2010 Other Segment [Member]	Dec. 31, 2009 Other Segment [Member] Corporate Restructuring [Member]		Jun. 30, 2009 Business Services Company [Member] EmployeePositions	Dec. 31, 2009 Business Services Company [Member] Corporate Restructuring [Member]		Dec. 31, 2011 Business Services Company [Member] Plant Retirements [Member]	Dec. 31, 2010 Business Services Company [Member] Plant Retirements [Member]	Dec. 31, 2009 Business Services Company [Member] Plant Retirements [Member]
Total Severance Benefits Costs [Abstract]
Severance benefits expense																$ 11,000,000	[1],[2]	$ 4,000,000	$ 4,000,000	$ 7,000,000				$ 19,000,000	[1],[2]			$ 3,000,000	[1],[2]			$ 1,000,000	[1],[2]		$ 34,000,000	[1],[2]	$ 4,000,000	$ 4,000,000	$ 7,000,000
Restructuring Charges [Abstract]
Severance expense billed through intercompany allocations									7,000,000														4,000,000				2,000,000
Contractual termination benefit expense				4,000,000																			2,000,000
Stock compensation severance benefit expense									1,000,000														1,000,000
Corporate Restructuring Severance Benefit Obligation [Line Items]
Cash payments		(1,000,000)	(18,000,000)					(3,000,000)														(7,000,000)				(1,000,000)				(1,000,000)	(7,000,000)
Severance benefit obligation - ending balance		0																												0
Corporate Restructuring Positions Eliminated [Abstract]
Positions eliminated due to restructuring	500																				100													400
Corporate Restructuring Program Severance Charges [Abstract]
Original severance cost estimate	40,000,000
Severance cost estimate adjustment				(6,000,000)	(10,000,000)	4,000,000
Plant Retirements Reserve [Line Items]
Severance benefit obligation - beginning balance		1,000,000	19,000,000				7,000,000	3,000,000														7,000,000				1,000,000				1,000,000	8,000,000
Severance charges recorded							4,000,000	4,000,000
Cash payments							(4,000,000)	(1,000,000)
Other adjustments								(3,000,000)
Severance benefit obligation - ending balance			1,000,000	19,000,000			7,000,000	7,000,000	3,000,000	7,000,000													7,000,000				1,000,000				1,000,000
Plant Retirements Costs [Abstract]
Plant retirement costs incurred										32,000,000
Severance benefits expense related to plant retirements										13,000,000	4,000,000	3,000,000
Inventory write down related to plant retirements				17,000,000					17,000,000	17,000,000
Plant shut-down costs										2,000,000				2,000,000
Total expected plant retirement costs							37,000,000				14,000,000		17,000,000	6,000,000
Plant Retirement Positions Eliminated [Abstract]
Positions eliminated due to plant retirements							253
Coal-fired generation units to be retired									3
Oil/gas-fired generation unit to be retired									1
Plant Retirements Reliability Must Run Revenue [Abstract]
Monthly revenue during reliability-must-run period															$ 6,000,000

[1] The amounts above include $7 million, $4 million, and $2 million at Generation, ComEd and PECO, respectively, for amounts billed through intercompany allocations for the year ended December 31, 2009.

[2] The severance benefits costs include $1 million of stock compensation expense collectively at Generation and ComEd for which the obligation is recorded in equity for the year ended December 31, 2009. Severance benefits also include $4 million and $2 million at Exelon and ComEd, respectively, of contractual termination benefits expense for which the obligation is recorded in other postretirement benefits.