Summary of Significant Accounting Policies (New Accounting Guidance) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash		$ 41	$ 18
Service cost		169
Non-service costs		72
SCE
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash		1
Service cost		164
Non-service costs		$ 84
SCE | Sales
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales from tariff offerings, percentage of total operating revenues	95.00%