Fair Value Measurements (Level 3 Rollforward) (Details) - Southern California Edison - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities Transfered Out Of Derivatives		$ 914
Level 3
Fair Value Disclosures Level 3 [Roll Forward]
Fair value of net assets (liabilities) at beginning of period	$ 101		$ (1,089)
Total realized/unrealized gains (losses):
Included in regulatory assets and liabilities	(20)		(77)
Fair value of net assets (liabilities) at end of period2	81		(1,166)
Change during the period in unrealized losses related to assets and liabilities held at the end of the period	$ 5		$ (102)