Derivative Instruments (Balance Sheet Disclosures) (Details) - SCE - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Net Liability
Reclassified derivative liabilities	$ 914
Commodity derivative contracts | Electric Utility
Derivative Assets
Gross amounts recognized		$ 111	$ 75
Gross amounts offset in the consolidated balance sheets		(1)	(1)
Cash collateral posted		0	0
Net amounts presented in the consolidated balance sheets		110	74
Offsetting Derivative Liabilities [Abstract]
Gross amounts recognized		3	1,158
Gross amounts offset in the consolidated balance sheets		(1)	(1)
Cash collateral posted		(1)	0
Net amounts presented in the consolidated balance sheets		1	1,157
Net Liability
Gross amounts recognized		108	(1,083)
Gross amounts offset in the consolidated balance sheets		0	0
Cash collateral posted		1	0
Net amounts presented in the consolidated balance sheets		109	(1,083)
Commodity derivative contracts | Derivative Assets, Short-Term | Electric Utility
Derivative Assets
Gross amounts recognized		106	74
Gross amounts offset in the consolidated balance sheets		(1)	(1)
Cash collateral posted		0	0
Net amounts presented in the consolidated balance sheets		105	73
Commodity derivative contracts | Derivative Assets, Long-Term | Electric Utility
Derivative Assets
Gross amounts recognized		5	1
Gross amounts offset in the consolidated balance sheets		0	0
Cash collateral posted		0	0
Net amounts presented in the consolidated balance sheets		5	1
Commodity derivative contracts | Derivative Liability, Short-Term | Electric Utility
Offsetting Derivative Liabilities [Abstract]
Gross amounts recognized		3	217
Gross amounts offset in the consolidated balance sheets		(1)	(1)
Cash collateral posted		(1)	0
Net amounts presented in the consolidated balance sheets		1	216
Commodity derivative contracts | Derivative Liability, Long-Term | Electric Utility
Offsetting Derivative Liabilities [Abstract]
Gross amounts recognized		0	941
Gross amounts offset in the consolidated balance sheets		0	0
Cash collateral posted		0	0
Net amounts presented in the consolidated balance sheets		$ 0	941
Commodity derivative contracts | Other Current Liabilities
Net Liability
Cash collateral			$ 2