Fair Value Measurements (Carrying Amount And Fair Value Of Financial Instruments) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt financial instrument	$ 349	$ 349
Energy recovery bonds (Note 4)	110	423
Fair Value [Member] | Fair Value Measurements, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt financial instrument	376	380
Energy recovery bonds (Note 4)	111	433
Pacific Gas And Electric Company [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt financial instrument	11,644	10,545
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	$ 14,151	$ 12,543