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Related Party Transactions (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Related Party Transaction [Line Items]      
Money pool borrowings $ 570,000,000 $ 0  
Dividends paid to parent 601,000,000 643,000,000 $ 43,000,000
Operation And Maintenance Expense [Member] | CenterPoint Energy [Member]      
Related Party Transaction [Line Items]      
Corporate services charge 128,000,000 125,000,000 118,000,000
Operation And Maintenance Expense [Member] | CenterPoint Houston [Member]      
Related Party Transaction [Line Items]      
Corporate services charge 17,000,000 15,000,000 18,000,000
Other revenues from transactions with related party $ (8,000,000) $ (7,000,000) $ (6,000,000)