Investments (Amortized Cost and Fair Value of Nuclear Decommissioning Trusts) (Details) - Southern California Edison - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	$ 2,778	$ 2,784
Fair Value	4,415	4,242
Stocks
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	290	319
Fair Value	1,655	1,547
Municipal bonds
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	612	659
Fair Value	738	766
U.S. government and agency securities
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	1,220	1,131
Fair Value	1,298	1,191
Corporate bonds
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	545	600
Fair Value	609	659
Short-term investments and receivables/payables
Nuclear Decommissioning Trusts Disclosures
Amortized Cost	111	75
Fair Value	$ 115	79
Repurchase agreement		$ 114