Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 66,829		$ 61,043
Less: accumulated depreciation	14,742	[1]	13,713	[1]
Property, plant and equipment, net	52,087		47,330
Nuclear fuel - work in progress	1,003		947
Buildings under capital lease	15		23
Original cost basis for buildings	52		59
Accumulated depreciation for buildings	37		36
Accumulated amortization of nuclear fuel	2,673		2,371
Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	30,157		28,123
Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	90 years
Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	22,911		20,420
Electric Generation Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	56 years
Electric Generation Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	1 year
Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	3,505		3,296
Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	90 years
Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,169		1,101
Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years
Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,947	[2]	5,196	[2]
Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	8 years	[2]
Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	1 year	[2]
Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	2,167		1,890
Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	973	[3]	1,017	[3]
Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years	[3]
Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years	[3]
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	30,557		27,145
Less: accumulated depreciation	7,612	[4]	7,034	[4]
Property, plant and equipment, net	22,945		20,111
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	22,911		20,420
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	56 years
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	1 year
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,947	[2]	5,196	[2]
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	8 years	[2]
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	1 year	[2]
Exelon Generation Co L L C [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,404		1,129
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	295	[5]	400	[5]
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	31 years	[5]
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	6 years	[5]
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	19,225		17,850
Less: accumulated depreciation	3,432		3,184
Property, plant and equipment, net	15,793		14,666
Buildings under capital lease			8
Original cost basis for buildings	8
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	18,884		17,334
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	80 years
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Commonwealth Edison Co [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	276		456
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	65	[6]	60	[6]
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years	[6]
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	39 years	[6]
PECO Energy Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	9,718		9,319
Less: accumulated depreciation	2,917		2,935
Property, plant and equipment, net	6,801		6,384
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,886		6,669
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	65 years
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
PECO Energy Co [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	2,039		1,932
PECO Energy Co [Member] | Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	70 years
PECO Energy Co [Member] | Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	618		600
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
PECO Energy Co [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	154		101
PECO Energy Co [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years	[7]
Total property, plant and equipment	21	[7]	17	[7]
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	9,072		8,566
Less: accumulated depreciation	2,868		2,702
Property, plant and equipment, net	6,204		5,864
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	6,339		6,100
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	90 years
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,761		1,660
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	90 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	623		578
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Baltimore Gas and Electric Company [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	317		196
Baltimore Gas and Electric Company [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	20 years	[7]
Total property, plant and equipment	$ 32	[7]	$ 32	[7]

[1] Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,673 million and $2,371 million as of December 31, 2014 and 2013, respectively.

[2] Includes nuclear fuel that is in the fabrication and installation phase of $1,003 million and $947 million at December 31, 2014 and 2013, respectively.

[3] Includes Generation’s buildings under capital lease with a net carrying value of $15 million and $23 million at December 31, 2014 and 2013, respectively. The original cost basis of the buildings was $52 million and $59 million, and total accumulated amortization was $37 million and $36 million, as of December 31, 2014 and 2013, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2014 and 2013, of $8 million. The original cost basis of the buildings was $8 million and total accumulated amortization was immaterial as of December 31, 2014 and 2013, respectively. Includes land held for future use and non utility property at ComEd, PECO, and BGE of $57 million, $21 million, and $32 million, respectively. These balances also include capitalized acquisition, development and exploration costs of $242 million related to oil and gas production activities at Generation.

[4] Includes accumulated amortization of nuclear fuel in the reactor core of $2,673 million and $2,371 million as of December 31, 2014 and 2013, respectively.

[5] Includes buildings under capital lease with a net carrying value of $15 million and $23 million at December 31, 2014 and 2013, respectively. The original cost basis of the buildings was $52 million and $59 million, and total accumulated amortization was $37 million and $36 million, as of December 31, 2014 and 2013, respectively. These balances also include capitalized acquisition, development and exploration costs of $242 million related to oil and gas production activities.

[6] Includes buildings under capital lease with a net carrying value at both of December 31, 2014 and 2013, of $8 million. The original cost basis of the buildings was $8 million and total accumulated amortization was immaterial as of December 31, 2014 and 2013, respectively.

[7] Represents land held for future use and non utility property.