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Long-term Debt (Details) (USD $)
In Millions, unless otherwise specified
1 Months Ended 9 Months Ended 1 Months Ended
Jan. 31, 2012
tranches
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Line of Credit [Member]
Dec. 31, 2011
Line of Credit [Member]
Aug. 31, 2012
CenterPoint Houston [Member]
Bonds General Mortgage Due 2022 [Member]
Aug. 31, 2012
CenterPoint Houston [Member]
Bonds General Mortgage Due 2042 [Member]
Aug. 31, 2012
CenterPoint Houston [Member]
Bonds General Mortgage Due January 2014 [Member]
Aug. 31, 2012
CenterPoint Houston [Member]
Bonds General Mortgage Due March 2014 [Member]
Aug. 31, 2012
CenterPoint Houston [Member]
Bonds General Mortgage Due 2014 [Member]
Debt Instrument [Line Items]                    
Amount Of Transition Bonds Issued To Recover Additional True Up Costs $ 1,695                  
Line of Credit Facility, Maximum Borrowing Capacity       300 300          
Loans Outstanding       0 0          
Letters Of Credit Outstanding       4 4          
Number of tranches of transition bonds 3                  
Minimum Interest Rate On Transition Bonds 0.9012%                  
Maximum Interest Rate On Transition Bonds 3.0282%                  
Revolving credit facility borrowing rate       London Interbank Offered Rate plus 125            
Percentage on limitation of debt to total capitalization under covenant (in hundredths)       65.00%            
First Mortgage Bonds Used as Collateral   151 151              
General mortgage bonds used as collateral   408 508              
Debt Instrument, Face Amount           300 500      
Debt Instrument, Interest Rate, Stated Percentage           2.25% 3.55% 5.75% 7.00%  
Extinguishment Of Debt Purchase Price Percentage Of Principal               107.332% 109.397%  
Extinguishment of Debt, principal amount               300 500  
Number of general mortgage bond series called for redemption                   2
Redemption Premium                   $ 69