Equity (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Common Stock Value	$ 11,440	$ 11,282
Pacific Gas And Electric Company [Member]
Common Stock Value	$ 1,322	$ 1,322
Equity Contract [Member]
Equity Distribution Agreement, shares issued	1,300,000
Remaining equity distribution agreement amount	$ 350
Fees and commissions	1
Stock Issued During Period Value Under Equity Distribution Agreement	$ 74
401K Plan, DRSPP, and Shared Based Compensation Plans [Member]
Stock issued during period for stock options exercised and under 401(K) plan and DRSPP, shares	2,300,000
Stock Issued During Period Value Stock Options Exercised	$ 72