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Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 73,814 $ 66,912
Less: accumulated depreciation [1] 16,375 14,742
Property, plant and equipment, net 57,439 52,170
Nuclear fuel - work in progress 1,266 1,003
Buildings under capital lease 13 15
Original cost basis for buildings 52  
Plant Held for Future Use Amount 57  
Accumulated depreciation for buildings 39 37
Accumulated amortization of nuclear fuel 2,861 2,673
Electric Transmission and Distribution Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 32,546 30,157
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 $ 25,615 22,911
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 $ 3,864 3,505
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 $ 1,149 1,169
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 [2] $ 6,384 5,947
Nuclear Fuel [Member] | Maximum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [2] 8 years  
Nuclear Fuel [Member] | Minimum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [2] 1 year  
Public Utilities Property Plant And Equipment Construction Work In Progress [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 3,075 2,167
Other Capitalized Property Plant and Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment [3] $ 1,181 1,056
Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [3] 50 years  
Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [3] 5 years  
Exelon Generation Co L L C [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 34,482 30,640
Less: accumulated depreciation [4] 8,639 7,612
Property, plant and equipment, net 25,843 23,028
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 25,615 22,911
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] $ 6,384 5,947
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [5] 8 years  
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [5] 1 year  
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 $ 2,017 1,404
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 [6] $ 466 378
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 [6] 31 years  
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] 6 years  
Commonwealth Edison Co [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 21,212 19,225
Less: accumulated depreciation 3,710 3,432
Property, plant and equipment, net 17,502 15,793
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 $ 20,576 18,884
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 $ 572 276
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment [7] $ 64 65
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 [7] 50 years  
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 [7] 39 years  
PECO Energy Co [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 10,242 9,718
Less: accumulated depreciation 3,101 2,917
Property, plant and equipment, net 7,141 6,801
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 7,230 6,886
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 $ 2,206 2,039
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 $ 631 618
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 $ 154 154
PECO Energy Co [Member] | Other Capitalized Property Plant and Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, useful life [8] 50 years  
Total property, plant and equipment [8] $ 21 21
Baltimore Gas and Electric Company [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment 9,613 9,072
Less: accumulated depreciation 3,016 2,868
Property, plant and equipment, net 6,597 6,204
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Total property, plant and equipment $ 6,663 6,339
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 $ 1,951 1,761
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 $ 655 623
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 $ 312 317
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 [9] 20 years  
Total property, plant and equipment [9] $ 32 $ 32
[1] Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,861 million and $2,673 million as of December 31, 2015 and 2014, respectively
[2] Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014, respectively.
[3] Includes Generation’s buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014, respectively. The original cost basis of the buildings was $52 million, and total accumulated amortization was $39 million and $37 million, as of December 31, 2015 and 2014, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at December 31, 2015 and 2014, of $7 million and $8 million, respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014, 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 $266 million and $242 million related to oil and gas production activities at Generation
[4] Includes accumulated amortization of nuclear fuel in the reactor core of $2,861 million and $2,673 million as of December 31, 2015 and 2014, respectively
[5] Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014, respectively
[6] Includes buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014, respectively. The original cost basis of the buildings was $52 million, and total accumulated amortization was $39 million and $37 million, as of December 31, 2015 and 2014, respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014, respectively.
[7] Includes buildings under capital lease with a net carrying value at December 31, 2015 and 2014 of $7 million and $8 million, respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014, respectively
[8] Represents land held for future use and non-utility property
[9] Represents land held for future use and non-utility property