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GENERAL INFORMATION AND OTHER FINANCIAL DATA - INCOME TAXES (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2017
Income Tax Expense And Effective Income Tax Rates Disclosure [Line Items]        
Federal tax rate 21.00%     35.00%
Pretax income $ 672   $ 755  
Income tax expense $ 289   $ 295 [1]  
ETR 43.00%   39.00%  
Equity earnings, before income tax $ 5   $ 3  
TCJA provisional income tax expense 25 $ 870    
Income tax expense from transactional effects of foreign currency and inflation 94   97  
Income tax expense from transactional effects of foreign currency and inflation net of noncontrolling interest 63   65  
Gain (loss) from foreign currency derivatives 44   65  
Gain (loss) from foreign currency derivatives after-tax 32   39  
San Diego Gas and Electric Company [Member]        
Income Tax Expense And Effective Income Tax Rates Disclosure [Line Items]        
Pretax income 225   247  
Income tax expense $ 56   $ 90 [1]  
ETR 25.00%   36.00%  
TCJA provisional income tax expense $ (38)      
Southern California Gas Company [Member]        
Income Tax Expense And Effective Income Tax Rates Disclosure [Line Items]        
Pretax income 284   $ 301  
Income tax expense $ 59   $ 98 [1]  
ETR 21.00%   33.00%  
TCJA provisional income tax expense $ 5      
[1] As adjusted for the retrospective adoption of ASU 2017-07, which we discuss in Note 2, and a reclassification to conform to current year presentation, which we discuss in Note 1.