Fair Value Measurements (Level 3 Rollforward) (Details) - Southern California Edison - Level 3 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities	$ 914		$ 914
Fair Value Disclosures Level 3 [Roll Forward]
Fair value of net liabilities at beginning of period	(1,012)	$ (1,170)	(1,089)	$ (1,148)
Total realized/unrealized gains (losses):
Included in regulatory assets and liabilities	120	8	54	(14)
Settlements	0	(1)	0	(1)
Contract amendment	0	0	143	0
Normal purchase and normal sale designation	914	0	914	0
Fair value of net assets (liabilities) at end of period	22	(1,163)	22	(1,163)
Change during the period in unrealized losses related to assets and liabilities held at the end of the period	6	$ (57)	$ 6	$ (122)
Derivative contracts reclassified to other assets	$ 914