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Summary of Significant Accounting Policies (Nuclear Decommissioning and Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward    
Beginning balance $ 2,590  
Ending balance 2,908 $ 2,590
SCE    
Asset Retirement Obligation, Roll Forward    
Beginning balance 2,586 2,762
Accretion 166 157
Revisions 376 (165)
Liabilities settled (236) (168)
Ending balance $ 2,892 $ 2,586
Threshold period to be recognized as a loss for other-than-temporary impairment 2 months  
SCE | Palo Verde and San Onofre Units    
Asset Retirement Obligation, Roll Forward    
Recorded liability to decommission nuclear power facilities $ 2,600  
Estimated cost to decommission nuclear facilities $ 7,200  
Decommissioning cost escalated rates, low end (percent) 1.60%  
Decommissioning cost escalated rates, high end (percent) 7.50%  
Estimated annual net of tax earnings, low end (percent) 2.40%  
Estimated annual net of tax earnings, high end (percent) 3.80%