Fair Value Measurements (Level 3 Rollforward) (Details) - Southern California Edison - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Total realized/unrealized gains (losses):
Derivative liabilities reclassified to other liabilities		$ 914
Level 3
Fair Value Disclosures Level 3 [Roll Forward]
Fair value of net assets (liabilities) at beginning of period	$ 81	$ (1,012)	$ (1,166)	$ 101	$ (1,089)
Total realized/unrealized gains (losses):
Included in regulatory assets and liabilities	(29)		11	(49)	(66)
Contract amendment	0		143	0	143
Fair value of net assets (liabilities) at end of period	52		(1,012)	52	(1,012)
Change during the period in unrealized losses related to assets and liabilities held at the end of the period	$ 7		$ (12)	$ 7	$ (97)