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Property, Plant and Equipment, Net - MEC (Details) - MEC - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Property, Plant and Equipment [Line Items]    
Plant, net $ 18,672 $ 18,773
Construction work-in-progress 1,101 506
Property, plant and equipment, net 19,773 19,279
Regulated    
Property, Plant and Equipment [Line Items]    
Utility plant in service 26,110 25,669
Accumulated depreciation and amortization (7,444) (6,902)
Plant, net 18,666 18,767
Nonregulated    
Property, Plant and Equipment [Line Items]    
Accumulated depreciation and amortization (1) (1)
Plant, net 6 6
Nonregulated property gross $ 7 7
Nonregulated | Minimum    
Property, Plant and Equipment [Line Items]    
Useful life, other 20 years  
Nonregulated | Maximum    
Property, Plant and Equipment [Line Items]    
Useful life, other 50 years  
Electric Operations | Regulated    
Property, Plant and Equipment [Line Items]    
Generation $ 17,162 16,980
Transmission 2,415 2,365
Distribution $ 4,522 4,369
Electric Operations | Regulated | Minimum    
Property, Plant and Equipment [Line Items]    
Useful life, generation 20 years  
Useful life, transmission 52 years  
Useful life, distribution 20 years  
Electric Operations | Regulated | Maximum    
Property, Plant and Equipment [Line Items]    
Useful life, generation 70 years  
Useful life, transmission 75 years  
Useful life, distribution 75 years  
Natural Gas Processing Plant | Regulated    
Property, Plant and Equipment [Line Items]    
Distribution $ 2,011 $ 1,955
Natural Gas Processing Plant | Regulated | Minimum    
Property, Plant and Equipment [Line Items]    
Useful life, distribution 29 years  
Natural Gas Processing Plant | Regulated | Maximum    
Property, Plant and Equipment [Line Items]    
Useful life, distribution 75 years