Equity (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	May 02, 2013	Dec. 31, 2012
Common Stock Value	$ 9,212			$ 8,428
Proceeds From Issuance Of Common Stock	724	702
Equity distribution agreement amount			400
Pacific Gas And Electric Company [Member]
Common Stock Value	1,322			1,322
Equity contribution	835	715
Equity Contract [Member]
Common Stock Shares Issued	5,000,000
Common Stock Value	212		150
Net of fees and commissions	2
Underwritten Public Offering [Member]
Common Stock Shares Issued	7,000,000
Common Stock Value	300
Four Zero One K Plan DRSPP and Share Based Compensation Plans [Member]
Common Stock Shares Issued	6,000,000
Common Stock Value	212
May 2 2013 Equity Contract [Member]
Net of fees and commissions	$ 1