New And Significant Accounting Policies (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Public Utility, Property, Plant and Equipment [Line Items]
Benefits and customers payments received on tax equity agreements	$ 225
Residential And Commercial Retail Solar Energy Installations [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Payments made under tax equity agreements	396
Lease Payments And Investment Contributions [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Payments made under tax equity agreements	361
Pacific Gas And Electric Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Utility's equity investment in PERF	100.00%
PERF [Member]
Public Utility, Property, Plant and Equipment [Line Items]
PERF assets	156
PERF liabilities	$ 111