Fair Value Measurements (Level 3 Rollforward) (Details) - SCE - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Total realized/unrealized gains:
Reclassified derivative liabilities	$ 914
Level 3
Fair Value Disclosures Level 3 [Roll Forward]
Fair value of net liabilities at beginning of period		$ (1,089)	$ (1,148)
Total realized/unrealized gains:
Included in regulatory assets and liabilities		133	59
Contract amendment		143	0
Normal purchase and normal sale designation		914	0
Fair value of net assets (liabilities) at end of period		101	(1,089)
Change during the period in unrealized gains and losses related to assets and liabilities held at the end of the period		$ 100	$ (70)
Reclassified derivative liabilities	$ 914