Equity (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended
	Mar. 20, 2012	Sep. 30, 2012	Sep. 30, 2012 Pacific Gas And Electric Company [Member]	Sep. 30, 2011 Pacific Gas And Electric Company [Member]	Sep. 30, 2012 Equity Contract [Member]
Stock issued during period for stock options exercised and under 401(K) plan and DRSPP		5,446,542
Cash proceeds from employee stock options exercised		$ 214			$ 234
Equity Distribution Agreement, shares issued		5,446,760
Net of fees and commissions		2
Equity distribution agreement amount		64
Sale of common stock in an underwritten public offering	5,900,000
Cash proceeds from sale of common shares in an underwritten public offering	254	720
Common equity ratio percentage		52.00%
Debt and preferred stock ratio percentage		48.00%
Equity contribution			$ 715	$ 350