Commitments And Contingencies (Environmental Remediation Liability Composed) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Topock natural gas compressor station	$ 299	$ 300
Hinkley natural gas compressor station	135	140
Former manufactured gas plant sites owned by the Utility or third parties	285	271
Utility-owned generation facilities (other than for fossil fuel-fired), other facilities, and third-party disposal sites	131	164
Fossil fuel-fired generation facilities and sites	108	94
Total environmental remediation liability	$ 958	$ 969