Commitments And Contingencies (Environmental Remediation Liability Composed) (Detail) - USD ($) $ in Millions	Dec. 31, 2017		Dec. 31, 2016
Topock natural gas compressor station	$ 334		$ 299
Hinkley natural gas compressor station	147		135
Former manufactured gas plant sites owned by the Utility or third parties	320	[1]	285
Utility-owned generation facilities (other than for fossil fuel-fired), other facilities, and third-party disposal sites	115	[2]	131
Fossil fuel-fired generation facilities and sites	123	[3]	108
Total environmental remediation liability	$ 1,039		$ 958

[1] Primarily driven by the following sites: Vallejo, SF East Harbor, Napa, and SF North Beach

[2] Primarily driven by the Shell Pond site

[3] Primarily driven by the SF Potrero Power Plant site