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Property, Plant and Equipment Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment $ 90,724 $ 95,266 $ 90,724  
Less: accumulated depreciation [1] 19,169 21,064 19,169  
Property, plant and equipment, net 71,555 74,202 71,555  
Impairment of Long-Lived Assets Held-for-use   573 306 $ 36
Successor [Member]        
Property, Plant and Equipment [Line Items]        
Impairment of Long-Lived Assets Held-for-use 0      
Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 45,698 $ 49,506 45,698  
Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   90 years    
Electric—generation        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 27,193 $ 29,019 27,193  
Electric—generation | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   2 years    
Electric—generation | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   56 years    
Gas Distribution Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 4,642 $ 5,050 4,642  
Gas Distribution Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Gas Distribution Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   90 years    
Common—electric and gas        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 1,312 $ 1,447 1,312  
Common—electric and gas | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Common—electric and gas | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Nuclear Fuel [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [2] 6,546 $ 6,420 6,546  
Nuclear Fuel [Member] | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   1 year    
Nuclear Fuel [Member] | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   8 years    
Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 4,306 $ 2,825 4,306  
Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [3] 1,027 $ 999 1,027  
Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   2 years    
Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   50 years    
Exelon Generation Co L L C [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 36,147 $ 36,334 36,147  
Less: accumulated depreciation [4] 10,562 11,428 10,562  
Property, plant and equipment, net 25,585 24,906 25,585  
Nuclear fuel - work in progress 1,326 1,196 1,326  
Capital Leases, Balance Sheet, Assets by Major Class, Net 10 7 10  
Capital Leased Assets, Gross 52 47 52  
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation 42 40 42  
Property, Plant, and Equipment, Fair Value Disclosure 17 0 17  
Impairment of Long-Lived Assets Held-for-use   510 243 12
Exelon Generation Co L L C [Member] | Electric—generation        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 27,193 29,019 27,193  
Impairment of Long-Lived Assets Held-for-use   11    
Assets Held-for-sale, Not Part of Disposal Group, Current   $ 6    
Exelon Generation Co L L C [Member] | Electric—generation | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   2 years    
Exelon Generation Co L L C [Member] | Electric—generation | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   56 years    
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [5] 6,546 $ 6,420 6,546  
Less: accumulated depreciation 3,186 $ 3,159 3,186  
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   1 year    
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   8 years    
Exelon Generation Co L L C [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 2,332 $ 838 2,332  
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [6] 76 $ 57 76  
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   2 years    
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   3 years    
Commonwealth Edison Co [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 23,272 $ 24,992 23,272  
Less: accumulated depreciation 3,937 4,269 3,937  
Property, plant and equipment, net 19,335 20,723 19,335  
Capital Leases, Balance Sheet, Assets by Major Class, Net 7 7 7  
Capital Leased Assets, Gross 8 8 8  
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation 1 1 1  
Plant Held for Future Use Amount   44    
Commonwealth Edison Co [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 22,636 $ 24,423 22,636  
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   80 years    
Commonwealth Edison Co [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 569 $ 517 569  
Commonwealth Edison Co [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [7],[8] 67 $ 52 67  
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   36 years    
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   50 years    
PECO Energy Co [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 10,818 $ 11,464 10,818  
Less: accumulated depreciation 3,253 3,411 3,253  
Property, plant and equipment, net 7,565 8,053 7,565  
Plant Held for Future Use Amount   21    
PECO Energy Co [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 7,591 $ 7,975 7,591  
PECO Energy Co [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
PECO Energy Co [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   65 years    
PECO Energy Co [Member] | Gas Distribution Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 2,348 $ 2,504 2,348  
PECO Energy Co [Member] | Gas Distribution Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
PECO Energy Co [Member] | Gas Distribution Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   70 years    
PECO Energy Co [Member] | Common—electric and gas        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 670 $ 710 670  
PECO Energy Co [Member] | Common—electric and gas | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
PECO Energy Co [Member] | Common—electric and gas | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   50 years    
PECO Energy Co [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 188 $ 254 188  
PECO Energy Co [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [9] 21 $ 21 21  
Average Service Life (years)   50 years    
Baltimore Gas and Electric Company [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 10,294 $ 11,007 10,294  
Less: accumulated depreciation 3,254 3,405 3,254  
Property, plant and equipment, net 7,040 7,602 7,040  
Plant Held for Future Use Amount   26    
Impairment of Long-Lived Assets Held-for-use   7 52 0
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 7,067 $ 7,464 7,067  
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   90 years    
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 2,170 $ 2,379 2,170  
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   90 years    
Baltimore Gas and Electric Company [Member] | Common—electric and gas        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 707 $ 771 707  
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   40 years    
Baltimore Gas and Electric Company [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 318 $ 367 318  
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [10] 32 $ 26 32  
Average Service Life (years)   20 years    
Pepco Holdings LLC [Member] | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 11,793 $ 12,985 11,793  
Less: accumulated depreciation 195 487 195  
Property, plant and equipment, net 11,598 12,498 11,598  
Impairment of Long-Lived Assets Held-for-use   52    
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 10,315 $ 11,517 10,315  
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 414 $ 449 414  
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Pepco Holdings LLC [Member] | Common—electric and gas | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 65 $ 82 65  
Pepco Holdings LLC [Member] | Common—electric and gas | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Pepco Holdings LLC [Member] | Common—electric and gas | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Pepco Holdings LLC [Member] | Construction work in progress | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 892 $ 835 892  
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Successor [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [11] 107 $ 102 107  
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   3 years    
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   43 years    
Potomac Electric Power Company [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 8,621 $ 9,178 8,621  
Less: accumulated depreciation 3,050 3,177 3,050  
Property, plant and equipment, net 5,571 6,001 5,571  
Plant Held for Future Use Amount   59    
Impairment of Long-Lived Assets Held-for-use   14 0 0
Potomac Electric Power Company [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 8,018 $ 8,646 8,018  
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Potomac Electric Power Company [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 537 $ 473 537  
Potomac Electric Power Company [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [12] 66 $ 59 66  
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   25 years    
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   33 years    
Delmarva Power and Light Company [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 4,448 $ 4,826 4,448  
Less: accumulated depreciation 1,175 1,247 1,175  
Property, plant and equipment, net 3,273 3,579 3,273  
Plant Held for Future Use Amount   15    
Impairment of Long-Lived Assets Held-for-use   6 0 0
Delmarva Power and Light Company [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 3,574 $ 3,875 3,574  
Delmarva Power and Light Company [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Delmarva Power and Light Company [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   70 years    
Delmarva Power and Light Company [Member] | Gas Distribution Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 580 $ 614 580  
Delmarva Power and Light Company [Member] | Gas Distribution Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Delmarva Power and Light Company [Member] | Gas Distribution Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Delmarva Power and Light Company [Member] | Common—electric and gas        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 115 $ 117 115  
Delmarva Power and Light Company [Member] | Common—electric and gas | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Delmarva Power and Light Company [Member] | Common—electric and gas | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   75 years    
Delmarva Power and Light Company [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 163 $ 205 163  
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [13] 16 $ 15 16  
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   10 years    
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   43 years    
Atlantic City Electric Company [Member]        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 3,537 $ 3,772 3,537  
Less: accumulated depreciation 1,016 1,066 1,016  
Property, plant and equipment, net 2,521 2,706 2,521  
Plant Held for Future Use Amount   27    
Impairment of Long-Lived Assets Held-for-use   7 0 $ 0
Atlantic City Electric Company [Member] | Electric—transmission and distribution        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 3,341 $ 3,607 3,341  
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   5 years    
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   60 years    
Atlantic City Electric Company [Member] | Construction work in progress        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment 169 $ 138 169  
Atlantic City Electric Company [Member] | Other Property Plant and Equipment        
Property, Plant and Equipment [Line Items]        
Total property, plant and equipment [14] $ 27 $ 27 $ 27  
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   13 years    
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Average Service Life (years)   15 years    
[1] Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $3,159 million and $3,186 million as of December 31, 2017 and 2016, respectively.
[2] Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016, respectively.
[3] Includes Generation’s buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016, respectively. The original cost basis of the buildings was $47 million and $52 million, and total accumulated amortization was $40 million and $42 million, as of December 31, 2017 and 2016, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2017 and 2016, of $7 million. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016. Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $44 million, $21 million, $26 million, $59 million, $15 million and $27 million, respectively, at December 31, 2017. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016, respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017.
[4] Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million and $3,186 million as of December 31, 2017 and 2016, respectively
[5] Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016, respectively
[6] Includes buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016, respectively. The original cost basis of the buildings was $47 million and $52 million, and total accumulated amortization was $40 million and $42 million, as of December 31, 2017 and 2016, respectively.
[7] Includes buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 of $7 million. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016
[8] Includes land held for future use and non-utility property.
[9] Represents land held for future use and non-utility property.
[10] Represents land held for future use and non-utility property
[11] Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[12] Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[13] Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[14] Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.