Derivative Instruments (Balance Sheet Disclosures) (Details) - Southern California Edison Company - Commodity derivative contracts - Electric Utility - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Assets
Gross amounts recognized	$ 97	$ 111
Gross amounts offset in the consolidated balance sheets	(2)	(1)
Cash collateral posted	0	0
Net amounts presented in the consolidated balance sheets	95	110
Derivative Liabilities
Gross amounts recognized	4	3
Gross amounts offset in the consolidated balance sheets	(2)	(1)
Cash collateral posted	(1)	(1)
Net amounts presented in the consolidated balance sheets	1	1
Net Asset
Gross amounts recognized	93	108
Gross amounts offset in the consolidated balance sheets	0	0
Cash collateral posted	1	1
Net amounts presented in the consolidated balance sheets	94	109
Derivative Assets, Short-Term
Derivative Assets
Gross amounts recognized	94	106
Gross amounts offset in the consolidated balance sheets	(2)	(1)
Cash collateral posted	0	0
Net amounts presented in the consolidated balance sheets	92	105
Derivative Assets, Long-Term
Derivative Assets
Gross amounts recognized	3	5
Gross amounts offset in the consolidated balance sheets	0	0
Cash collateral posted	0	0
Net amounts presented in the consolidated balance sheets	3	5
Derivative Liability, Short-Term
Derivative Liabilities
Gross amounts recognized	4	3
Gross amounts offset in the consolidated balance sheets	(2)	(1)
Cash collateral posted	(1)	(1)
Net amounts presented in the consolidated balance sheets	1	1
Derivative Liability, Long-Term
Derivative Liabilities
Gross amounts recognized	0	0
Gross amounts offset in the consolidated balance sheets	0	0
Cash collateral posted	0	0
Net amounts presented in the consolidated balance sheets	$ 0	$ 0