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Fair Value Measurements (Carrying Amount And Fair Value Of Financial Instruments) (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Carrying Amount [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt financial instrument $ 350 $ 349
Fair Value [Member] | Fair Value Measurements, Level 2 [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt financial instrument 363 371
Pacific Gas And Electric Company [Member] | Carrying Amount [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt financial instrument 11,933 11,645
Pacific Gas And Electric Company [Member] | Fair Value [Member] | Fair Value Measurements, Level 2 [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt financial instrument $ 13,076 $ 13,946