Equity (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013	Mar. 31, 2013 Pacific Gas And Electric Company [Member]	Mar. 31, 2012 Pacific Gas And Electric Company [Member]	Mar. 31, 2013 Equity Contract [Member]
Sale of common stock in an underwritten public offering	7,200,000
Cash proceeds from sale of common shares in an underwritten public offering	$ 300
Stock issued during period for stock options exercised and under 401(K) plan and DRSPP		2,109,980
Stock Issued During Period Value Stock Options Exercised		63
Equity Distribution Agreement, shares issued					1,480,900
Equity distribution agreement amount					63
Common equity ratio percentage		52.00%
Debt and preferred stock ratio percentage		48.00%
Equity contribution			$ 370	$ 385