Supplemental Financial Information (Details) (USD $)	1 Months Ended	3 Months Ended										12 Months Ended																												3 Months Ended										12 Months Ended						25 Months Ended		12 Months Ended																		3 Months Ended										12 Months Ended																							3 Months Ended										12 Months Ended
	Oct. 31, 2000	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2011 Financing Trusts [Member]	Dec. 31, 2010 Financing Trusts [Member]	Dec. 31, 2009 Financing Trusts [Member]	Dec. 31, 2011 NuStart Energy Development [Member]	Dec. 31, 2010 NuStart Energy Development [Member]	Dec. 31, 2009 NuStart Energy Development [Member]	Dec. 31, 2011 Capital Leases Net Investment In Direct Financing Leases [Member]	Dec. 31, 2010 Capital Leases Net Investment In Direct Financing Leases [Member]	Dec. 31, 2011 Trust For Benefit Of Employees [Member]		Dec. 31, 2010 Trust For Benefit Of Employees [Member]		Dec. 31, 2011 Financing Trusts [Member]		Dec. 31, 2010 Financing Trusts [Member]		Dec. 31, 2010 NuStart Energy Development [Member]	Dec. 31, 2011 Keystone Fuels [Member]	Dec. 31, 2010 Keystone Fuels [Member]	Dec. 31, 2011 Conemaugh Fuels [Member]	Dec. 31, 2010 Conemaugh Fuels [Member]	Dec. 31, 2011 Sacramento Solar [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]		Sep. 30, 2011 Exelon Generation Co L L C [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member]		Sep. 30, 2010 Exelon Generation Co L L C [Member]	Jun. 30, 2010 Exelon Generation Co L L C [Member]	Mar. 31, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]		Dec. 31, 2009 Exelon Generation Co L L C [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Financing Trusts [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Financing Trusts [Member]	Dec. 31, 2009 Exelon Generation Co L L C [Member] Financing Trusts [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] NuStart Energy Development [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] NuStart Energy Development [Member]	Dec. 31, 2009 Exelon Generation Co L L C [Member] NuStart Energy Development [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member] Financing Trusts [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member] NuStart Energy Development [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Keystone Fuels [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Keystone Fuels [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Conemaugh Fuels [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member] Conemaugh Fuels [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Sacramento Solar [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member]		Sep. 30, 2011 Commonwealth Edison Co [Member]	Jun. 30, 2011 Commonwealth Edison Co [Member]	Mar. 31, 2011 Commonwealth Edison Co [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member]		Sep. 30, 2010 Commonwealth Edison Co [Member]	Jun. 30, 2010 Commonwealth Edison Co [Member]	Mar. 31, 2010 Commonwealth Edison Co [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member]		Dec. 31, 2009 Commonwealth Edison Co [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member] Financing Trusts [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Financing Trusts [Member]	Dec. 31, 2009 Commonwealth Edison Co [Member] Financing Trusts [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] NuStart Energy Development [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] NuStart Energy Development [Member]	Dec. 31, 2009 Commonwealth Edison Co [Member] NuStart Energy Development [Member]	Dec. 31, 2011 Commonwealth Edison Co [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2011 Commonwealth Edison Co [Member] Financing Trusts [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member] Financing Trusts [Member]		Dec. 31, 2010 Commonwealth Edison Co [Member] NuStart Energy Development [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Keystone Fuels [Member]	Dec. 31, 2010 Commonwealth Edison Co [Member] Conemaugh Fuels [Member]	Dec. 31, 2011 PECO Energy Co [Member]		Sep. 30, 2011 PECO Energy Co [Member]	Jun. 30, 2011 PECO Energy Co [Member]	Mar. 31, 2011 PECO Energy Co [Member]	Dec. 31, 2010 PECO Energy Co [Member]		Sep. 30, 2010 PECO Energy Co [Member]	Jun. 30, 2010 PECO Energy Co [Member]	Mar. 31, 2010 PECO Energy Co [Member]	Dec. 31, 2011 PECO Energy Co [Member]		Dec. 31, 2010 PECO Energy Co [Member]		Dec. 31, 2009 PECO Energy Co [Member]		Dec. 31, 2011 PECO Energy Co [Member] Financing Trusts [Member]	Dec. 31, 2010 PECO Energy Co [Member] Financing Trusts [Member]	Dec. 31, 2009 PECO Energy Co [Member] Financing Trusts [Member]	Dec. 31, 2011 PECO Energy Co [Member] NuStart Energy Development [Member]	Dec. 31, 2010 PECO Energy Co [Member] NuStart Energy Development [Member]	Dec. 31, 2009 PECO Energy Co [Member] NuStart Energy Development [Member]	Dec. 31, 2011 PECO Energy Co [Member] Low Risk [Member]	Dec. 31, 2010 PECO Energy Co [Member] Low Risk [Member]	Dec. 31, 2011 PECO Energy Co [Member] Medium Risk [Member]	Dec. 31, 2010 PECO Energy Co [Member] Medium Risk [Member]	Dec. 31, 2011 PECO Energy Co [Member] High Risk [Member]	Dec. 31, 2010 PECO Energy Co [Member] High Risk [Member]	Dec. 31, 2011 PECO Energy Co [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2010 PECO Energy Co [Member] Trust For Benefit Of Employees [Member]		Dec. 31, 2011 PECO Energy Co [Member] Financing Trusts [Member]		Dec. 31, 2010 PECO Energy Co [Member] Financing Trusts [Member]		Dec. 31, 2010 PECO Energy Co [Member] NuStart Energy Development [Member]	Dec. 31, 2010 PECO Energy Co [Member] Keystone Fuels [Member]	Dec. 31, 2010 PECO Energy Co [Member] Conemaugh Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments		$ 45,000,000					$ 39,000,000					$ 45,000,000		$ 39,000,000																$ 15,000,000	[1]	$ 15,000,000	[1]	$ 1,000,000	$ 13,000,000	$ 10,000,000	$ 16,000,000	$ 13,000,000	$ 1,000,000	$ 30,000,000					$ 24,000,000					$ 30,000,000		$ 24,000,000				$ 30,000,000												$ 0	[1]	$ 1,000,000	$ 13,000,000	$ 10,000,000	$ 16,000,000	$ 13,000,000	$ 1,000,000	$ 6,000,000					$ 6,000,000					$ 6,000,000		$ 6,000,000														$ 6,000,000	[1]	$ 6,000,000	[1]	$ 0	$ 0	$ 0	$ 8,000,000					$ 8,000,000					$ 8,000,000		$ 8,000,000																				$ 8,000,000	[1]	$ 8,000,000	[1]	$ 0	$ 0	$ 0
Other Investments [Abstract]
Other Investments																								656,000,000	629,000,000	65,000,000	[2]	64,000,000	[2]																																			11,000,000	[2]	11,000,000	[2]																															21,000,000	[2]	23,000,000	[2]																																				22,000,000	[2]	20,000,000	[2]
Total investments		766,000,000					732,000,000					766,000,000		732,000,000																										41,000,000					35,000,000					41,000,000		35,000,000				41,000,000																				27,000,000					29,000,000					27,000,000		29,000,000																					30,000,000					28,000,000					30,000,000		28,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Estimated residual value of leased assets	1,600,000,000	1,492,000,000					1,492,000,000					1,492,000,000		1,492,000,000
Less: unearned income		(836,000,000)					(863,000,000)					(836,000,000)		(863,000,000)
Net investment in long-term leases		656,000,000					629,000,000					656,000,000		629,000,000
Accrued Liabilities Current [Abstract]
Compensation-related accruals		520,000,000	[3]				465,000,000	[3]				520,000,000	[3]	465,000,000	[3]																									264,000,000	[3]				229,000,000	[3]				264,000,000	[3]	229,000,000	[3]			264,000,000	[3]																			127,000,000	[3]				110,000,000	[3]				127,000,000	[3]	110,000,000	[3]																				48,000,000	[3]				51,000,000	[3]				48,000,000	[3]	51,000,000	[3]
Taxes accrued		297,000,000					297,000,000					297,000,000		297,000,000																										241,000,000					38,000,000					241,000,000		38,000,000				241,000,000																				59,000,000					83,000,000					59,000,000		83,000,000																					5,000,000					9,000,000					5,000,000		9,000,000
Interest accrued		192,000,000					195,000,000					192,000,000		195,000,000																										56,000,000					76,000,000					56,000,000		76,000,000				56,000,000																				124,000,000					154,000,000					124,000,000		154,000,000																					27,000,000					30,000,000					27,000,000		30,000,000
Severance accrued		15,000,000					22,000,000					15,000,000		22,000,000																										9,000,000					10,000,000					9,000,000		10,000,000				9,000,000																				2,000,000					4,000,000					2,000,000		4,000,000																					1,000,000					1,000,000					1,000,000		1,000,000
Other accrued expenses		231,000,000	[4]				61,000,000					231,000,000	[4]	61,000,000																										209,000,000	[4]				38,000,000					209,000,000	[4]	38,000,000				209,000,000	[4]																			6,000,000					15,000,000					6,000,000		15,000,000																					2,000,000					4,000,000					2,000,000		4,000,000
Total accrued expenses		1,255,000,000					1,040,000,000					1,255,000,000		1,040,000,000																										779,000,000					391,000,000					779,000,000		391,000,000				779,000,000																				318,000,000					366,000,000					318,000,000		366,000,000																					83,000,000					95,000,000					83,000,000		95,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges		488,000,000					400,000,000					488,000,000		400,000,000																										915,000,000					1,013,000,000					915,000,000		1,013,000,000				915,000,000																				0					0					0		0																					0					0					0		0
Pension and non-pension postretirement benefit plans		(2,938,000,000)					(2,823,000,000)					(2,938,000,000)		(2,823,000,000)																										0										0						0																				0										0																							0					0					0		0
Accumulated unrealized gain (loss) on marketable securities							0							0																																																														(1,000,000)					(1,000,000)					(1,000,000)		(1,000,000)
Accumulated other comprehensive income (loss), net		(2,450,000,000)					(2,423,000,000)					(2,450,000,000)		(2,423,000,000)																										915,000,000					1,013,000,000					915,000,000		1,013,000,000				915,000,000																				(1,000,000)					(1,000,000)					(1,000,000)		(1,000,000)																					0					0					0		0
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables																																																																																																													21,000,000					22,000,000					21,000,000		22,000,000
Installment plan receivables uncollectible accounts reserve																																																																																																													(17,000,000)					(19,000,000)					(17,000,000)		(19,000,000)										(1,000,000)	(1,000,000)	(3,000,000)	(5,000,000)	(13,000,000)	(13,000,000)
Property, Plant And Equipment [Abstract]
Accumulated depreciation		10,959,000,000	[5]				10,064,000,000	[5]				10,959,000,000	[5]	10,064,000,000	[5]																									5,313,000,000	[6]				4,880,000,000	[6]				5,313,000,000	[6]	4,880,000,000	[6]			5,313,000,000	[6]																			2,750,000,000					2,428,000,000					2,750,000,000		2,428,000,000																					2,662,000,000					2,531,000,000					2,662,000,000		2,531,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(199,000,000)					(211,000,000)					(199,000,000)		(211,000,000)																										(29,000,000)					(32,000,000)					(29,000,000)		(32,000,000)				(29,000,000)																				(78,000,000)					(80,000,000)					(78,000,000)		(80,000,000)																					(92,000,000)					(99,000,000)					(92,000,000)		(99,000,000)
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)												649,000,000		665,000,000	[7]	647,000,000																																		158,000,000		145,000,000		69,000,000																																296,000,000		283,000,000		284,000,000																													128,000,000		168,000,000		179,000,000
Income taxes (net of refunds)												(457,000,000)		1,219,000,000		982,000,000																																		347,000,000		732,000,000		668,000,000																																(676,000,000)		15,000,000		63,000,000																													(65,000,000)		433,000,000		368,000,000
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs												542,000,000		581,000,000		536,000,000																																		249,000,000		268,000,000		240,000,000																																213,000,000		215,000,000		192,000,000																													32,000,000		46,000,000		47,000,000
Loss in equity method investments														0		27,000,000																																				0		3,000,000																																		0		0																															0		24,000,000
Provision for uncollectible accounts												121,000,000		108,000,000		149,000,000																																		0		1,000,000		2,000,000																																57,000,000		48,000,000		85,000,000																													64,000,000		59,000,000		63,000,000
Provision for obsolete inventory														12,000,000																																						12,000,000
Stock-based compensation costs												67,000,000		44,000,000		70,000,000
Other decommissioning-related activity												16,000,000	[8]	(91,000,000)	[9]	(163,000,000)	[7]																																	16,000,000	[8]	(91,000,000)	[9]	(163,000,000)	[7]
Energy-related options												137,000,000	[10]	(73,000,000)	[7]	46,000,000	[8]																																	137,000,000	[10]	(73,000,000)	[7]	46,000,000	[8]
ARO adjustment												0		(19,000,000)		(47,000,000)	[8]																																	0		(8,000,000)		(47,000,000)	[8]																															0		(10,000,000)																															0		(1,000,000)
Amortization of regulatory asset related to debt costs												21,000,000		24,000,000		25,000,000																																																																						18,000,000		20,000,000		21,000,000																													3,000,000		4,000,000		4,000,000
Accrual for Illinois utility distribution tax refund														(25,000,000)																																																																										(25,000,000)
Amortization of the regulatory liability related to the PURTA tax settlement																(2,000,000)																																																																																																											(2,000,000)
Under-recovered uncollectible accounts												14,000,000		(14,000,000)																																																																								14,000,000		(14,000,000)
APR SO2 allowances impairment												0		57,000,000																																				0		57,000,000
Other-than-temporary impairment to Rabbi trust investments														0		7,000,000	[11],[12]																																																																							0		7,000,000	[11],[12]
Inventory write down related to plant retirements																17,000,000																																						17,000,000		17,000,000
Net impact of the 2007 distribution rate case order																0																																						0																																				0
Discrete impacts from 2010 Rate Case Order												(32,000,000)																																																																										(32,000,000)
Bargain purchase gain Wolf Hollow acquisition		(36,000,000)										(36,000,000)																												(36,000,000)										(36,000,000)						(36,000,000)
Discrete impacts from EIMA												(82,000,000)	[13]																																																																									(82,000,000)	[13]
Reduction of guarantees																0
Other												14,000,000		5,000,000		(13,000,000)																																		55,000,000		16,000,000		6,000,000																																8,000,000		4,000,000		4,000,000																													1,000,000		0		5,000,000
Total other non-cash operating activities												(782,000,000)		(609,000,000)		(652,000,000)																																		(421,000,000)		(182,000,000)		(104,000,000)																																(196,000,000)		(238,000,000)		(309,000,000)																													(100,000,000)		(108,000,000)		(141,000,000)
Other Non-Cash Operating Activities Footnotes [Abstract]
Accrual for Illinois utility distribution tax refund														(25,000,000)																																																																										(25,000,000)
Reduction of guarantees																0
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs												(45,000,000)		61,000,000		23,000,000																																																																						(49,000,000)		58,000,000		13,000,000																													4,000,000		3,000,000		10,000,000
Other current assets												(101,000,000)		(18,000,000)		(2,000,000)																																		(23,000,000)		(16,000,000)		0																																(14,000,000)		12,000,000		0																													(15,000,000)		(19,000,000)		3,000,000
Other noncurrent assets and liabilities												126,000,000		(99,000,000)		(134,000,000)																																		(34,000,000)		(29,000,000)		(1,000,000)																																108,000,000		(203,000,000)	[14]	(76,000,000)	[14]																												25,000,000		94,000,000		(47,000,000)
Total changes in other assets and liabilities												(20,000,000)		(56,000,000)		(113,000,000)																																		(57,000,000)		(45,000,000)		(1,000,000)																																45,000,000		(133,000,000)		(63,000,000)																													14,000,000		78,000,000		(34,000,000)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Change in ARC												186,000,000		(428,000,000)		67,000,000																																		186,000,000		(428,000,000)		67,000,000
Capital expenditures not paid												96,000,000		34,000,000		70,000,000																																		125,000,000		13,000,000		97,000,000																																7,000,000		7,000,000		37,000,000																													(35,000,000)		14,000,000		4,000,000
Purchase accounting adjustments												0		9,000,000		9,000,000																																		0		9,000,000		9,000,000
Contingent consideration at fair value							32,000,000							32,000,000																															32,000,000							32,000,000
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures																																																																																																													51,000,000					28,000,000					51,000,000		28,000,000
Smart Grid Grant Reimbursements																																																																																																													56,000,000										56,000,000
Repurchase Agreements [Abstract]
Proceeds from nuclear decommissioning trust fund sales												6,139,000,000		3,764,000,000		4,292,000,000																																		6,139,000,000		3,764,000,000		4,292,000,000
Investment in nuclear decommissioning trust funds												(6,332,000,000)		(3,907,000,000)		(4,531,000,000)																																		(6,332,000,000)		(3,907,000,000)		(4,531,000,000)
Supplemental Financial Information Textuals [Abstract]
Payment to IRS														302,000,000
Estimated residual value of leased assets	1,600,000,000	1,492,000,000					1,492,000,000					1,492,000,000		1,492,000,000
Capital Leases Net Investment In Direct Financing Leases Prepayments Received	1,200,000,000
Operating revenues [Abstract]
Wholesale												7,717,000,000	[15]	5,934,000,000	[15]	5,469,000,000	[15]																																	8,837,000,000	[15]	8,986,000,000	[15]	8,905,000,000	[15]																															0	[15]	0	[15]	0	[15]																												32,000,000	[15]	44,000,000	[15]	26,000,000	[15]
Retail electric and gas												10,323,000,000	[15]	11,906,000,000	[15]	11,099,000,000	[15]																																	1,407,000,000	[15],[16]	1,004,000,000	[15],[16]	838,000,000	[15],[16]																															5,460,000,000	[15]	5,648,000,000	[15]	5,220,000,000	[15]																												3,463,000,000	[15]	5,262,000,000	[15]	5,049,000,000	[15]
Other												884,000,000	[15]	804,000,000	[15]	750,000,000	[15]																																	64,000,000	[15],[17]	35,000,000	[15],[17]	(40,000,000)	[15],[17]																															596,000,000	[15]	556,000,000	[15]	554,000,000	[15]																												225,000,000	[15]	213,000,000	[15]	236,000,000	[15]
Total operating revenues		3,991,000,000		5,295,000,000	4,587,000,000	5,052,000,000	4,494,000,000		5,291,000,000	4,398,000,000	4,461,000,000	18,924,000,000	[15]	18,644,000,000	[15]	17,318,000,000	[15]																							2,161,000,000		2,862,000,000	2,546,000,000	2,739,000,000	2,596,000,000		2,655,000,000	2,353,000,000	2,421,000,000	10,308,000,000	[15]	10,025,000,000	[15]	9,703,000,000	[15]																					1,362,000,000		1,784,000,000	1,444,000,000	1,466,000,000	1,372,000,000		1,918,000,000	1,499,000,000	1,415,000,000	6,056,000,000	[15]	6,204,000,000	[15]	5,774,000,000	[15]																		778,000,000		946,000,000	842,000,000	1,153,000,000	1,299,000,000		1,469,000,000	1,269,000,000	1,455,000,000	3,720,000,000	[15]	5,519,000,000	[15]	5,311,000,000	[15]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment												1,284,000,000		1,144,000,000		996,000,000																																		570,000,000		474,000,000		333,000,000																																502,000,000		473,000,000		446,000,000																													191,000,000		171,000,000		162,000,000
Regulatory assets												51,000,000		931,000,000		838,000,000																																		0		0		0																																40,000,000		43,000,000		48,000,000																													11,000,000		889,000,000	[18]	790,000,000	[18]
Nuclear fuel												755,000,000	[19]	672,000,000	[19]	558,000,000	[19]																																	755,000,000	[19]	672,000,000	[19]	558,000,000	[19]																															0		0		0																													0		0		0
Asset retirement obligation accretion												214,000,000	[20]	196,000,000	[20]	209,000,000	[20]																																	214,000,000	[20]	195,000,000	[20]	207,000,000	[20]																															0		1,000,000	[20]	1,000,000	[20]																												0		0	[20]	0	[20]
Total depreciation, amortization and accretion												2,304,000,000		2,943,000,000		2,601,000,000																																		1,539,000,000		1,341,000,000		1,098,000,000																																542,000,000		517,000,000		495,000,000																													202,000,000		1,060,000,000		952,000,000
Taxes Excluding Income And Excise Taxes [Abstract]
Taxes other than income - utility												443,000,000	[21]	476,000,000	[21]	481,000,000	[21]																																	27,000,000	[21]	0		0																																243,000,000	[21]	205,000,000	[21]	232,000,000	[21]																												173,000,000	[21]	271,000,000	[21]	249,000,000	[21]
Taxes other than income - real estate												177,000,000		175,000,000		157,000,000																																		146,000,000		142,000,000		127,000,000																																22,000,000		20,000,000		20,000,000																													9,000,000		13,000,000		10,000,000
Taxes other than income - payroll												123,000,000		121,000,000		114,000,000																																		71,000,000		70,000,000		65,000,000																																25,000,000		24,000,000		23,000,000																													13,000,000		12,000,000		12,000,000
Taxes other than income - other												42,000,000		36,000,000		26,000,000																																		20,000,000		18,000,000		13,000,000																																6,000,000		7,000,000		6,000,000																													10,000,000		7,000,000		5,000,000
Total taxes other than income												785,000,000		808,000,000		778,000,000																																		264,000,000		230,000,000		205,000,000																																296,000,000		256,000,000		281,000,000																													205,000,000		303,000,000		276,000,000
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments												(1,000,000)		0		(27,000,000)		0	0	(24,000,000)	(1,000,000)	0	(3,000,000)																											(1,000,000)		0		(3,000,000)				0	0	0	(1,000,000)	0	(3,000,000)																							0		0		0		0	0	0	0	0	0																						0		0		(24,000,000)		0	0	(24,000,000)	0	0	0
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units												177,000,000	[22]	176,000,000	[22]	126,000,000	[22]																																	177,000,000	[22]	176,000,000	[22]	126,000,000	[22]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units												45,000,000	[22]	51,000,000	[22]	29,000,000	[22]																																	45,000,000	[22]	51,000,000	[22]	29,000,000	[22]
Net unrealized losses on decommissioning trust funds - Regulatory Agreement Units												(74,000,000)		316,000,000		801,000,000																																		(74,000,000)		316,000,000		801,000,000
Net unrealized losses on decommissioning trust funds - Non-Regulatory Agreement												(4,000,000)		104,000,000		227,000,000																																		(4,000,000)		104,000,000		227,000,000
Regulatory offset to decommissioning trust fund-related activities												(130,000,000)	[23]	(394,000,000)	[23]	(746,000,000)	[23]																																	(130,000,000)	[23]	(394,000,000)	[23]	(746,000,000)	[23]
Net unrealized losses on pledged assets												48,000,000																																						48,000,000
Total decommissioning-related activities												62,000,000		253,000,000		437,000,000																																		62,000,000		253,000,000		437,000,000
Investment income												10,000,000		1,000,000		5,000,000																																		1,000,000																																				1,000,000		0		1,000,000																													3,000,000		1,000,000		4,000,000
Long-term lease income												28,000,000		27,000,000		26,000,000
Interest income related to uncertain income tax positions												53,000,000		0		50,000,000	[24]																																	31,000,000		0		0																																14,000,000		6,000,000		65,000,000	[24]																												1,000,000		0		5,000,000
Income related to termination of a gas supply guarantee																0																																						0
Realized gains on Rabbi Trust investments														1,000,000		5,000,000																																																																								1,000,000		5,000,000
Losses on early retirement of debt														0		117,000,000																																				0		71,000,000
Other-than-temporary impairment to Rabbi trust investments														0		(7,000,000)	[11],[12]																																																																							0		(7,000,000)	[11],[12]
AFUDC - equity												17,000,000		11,000,000		9,000,000																																																																						8,000,000		4,000,000		5,000,000																													9,000,000		7,000,000		4,000,000
Other												(7,000,000)		19,000,000		19,000,000																																		(8,000,000)		4,000,000		10,000,000																																6,000,000		13,000,000		10,000,000																													1,000,000		0		0
Other, net												199,000,000		312,000,000		427,000,000																																		122,000,000		257,000,000		376,000,000																																29,000,000		24,000,000		79,000,000																													14,000,000		8,000,000		13,000,000
Bargain purchase gain Wolf Hollow acquisition		$ (36,000,000)										$ (36,000,000)																												$ (36,000,000)										$ (36,000,000)						$ (36,000,000)

[1] Includes investments in financing trusts, which were not consolidated within the financial statements of Exelon. See Note 1 - Significant Accounting Policies for additional information.

[2] The Registrants' investments in these marketable securities are recorded at fair market value.

[3] Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

[4] Includes $184 million for amounts accrued related to Antelope Valley.

[5] 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.

[6] 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.

[7] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 12 - Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.

[8] Includes amounts reclassified to realized at settlement of contracts recorded to results of operations related to option premiums due to the settlement of underlying transactions.

[9] Excludes $167 million of interest paid to the IRS relating to a preliminary agreement reached during the third quarter of 2010. See Note 11 - Income Taxes for addition information.

[10] In May 2011, as a result of the 2010 Rate Case order, ComEd recorded one-time benefits to reestablish previously expensed plant balances and to recover previously incurred costs related to Exelon's 2009 restructuring plan. See Note 2 - Regulatory Matters for more information.

[11] During the second quarter of 2010, ComEd recorded a reduction of $25 million to taxes other than income to reflect management's estimate of future refunds for the 2008 and 2009 tax years associated with Illinois' utility distribution tax based on an analysis of past refunds and interpretations of the Illinois Public Utility Act. Historically, ComEd has recorded refunds of the Illinois utility distribution tax when received. ComEd believes it now has sufficient, reliable evidence to record and support an estimated receivable associated with the anticipated refund for the 2008 and 2009 tax years.

[12] ComEd recorded an other-than-temporary impairment to Rabbi trust investments during 2009.

[13] Includes the establishment of a regulatory asset, pursuant to EIMA, for the 2011 annual reconciliation in ComEd's distribution formula rate tariff and the deferral of costs associated with significant 2011 storms, partially offset by an accrual to fund a new Science and Technology Innovation Trust. See Note 2 - Regulatory Matters for more information.

[14] Relates primarily to a decrease in interest payable associated with a change in uncertain income tax positions. See Note 11 - Income Taxes for additional information.

[15] Includes operating revenues from affiliates.

[16] Generation's retail electric and gas operating revenues consist primarily of Exelon Energy Company, LLC. Generation's retail electric operating revenues are allocated among its reportable segments.

[17] Includes amounts recorded related to the Illinois Settlement Legislation.

[18] For PECO, primarily reflects CTC amortization.

[19] Included in fuel expense on the Registrants' Consolidated Statements of Operations.

[20] Included in operating and maintenance expense on the Registrants' Consolidated Statements of Operations.

[21] Generation's utility tax represents gross receipts tax related to its retail operations and ComEd's and PECO's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues, respectively. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants' Consolidated Statements of Operations.

[22] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[23] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 12 - Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.

[24] Primarily includes interest income at ComEd from the 2009 re-measurement of income tax uncertainties. See Note 11 - Income Taxes for additional information.