Long-term Debt (Details) (USD $) In Millions, unless otherwise specified								1 Months Ended							12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended								12 Months Ended		12 Months Ended	1 Months Ended
	Dec. 31, 2012		Jan. 31, 2012	Dec. 31, 2011		Aug. 31, 2012 Bonds General Mortgage Due 2022 [Member]	Aug. 31, 2012 Bonds General Mortgage Due 2042 [Member]	Aug. 31, 2012 Bonds General Mortgage Due January 2014 [Member]	Aug. 31, 2012 Bonds General Mortgage Due March 2014 [Member]	Aug. 31, 2012 Bonds General Mortgage Due 2014 [Member]	Dec. 31, 2012 First mortgage bonds 9.15% due 2021 [Member]		Dec. 31, 2011 First mortgage bonds 9.15% due 2021 [Member]		Dec. 31, 2012 General mortgage bonds 2.25% to 6.95% due 2013 to 2042 [Member]		Dec. 31, 2011 General mortgage bonds 2.25% to 6.95% due 2013 to 2042 [Member]		Dec. 31, 2012 Pollution control bonds 4.25% to 5.60% due 2017 to 2027 [Member]		Dec. 31, 2011 Pollution control bonds 4.25% to 5.60% due 2017 to 2027 [Member]		Dec. 31, 2012 System restoration bonds 1.833% to 4.243% due 2013 to 2022 [Member]		Dec. 31, 2011 System restoration bonds 1.833% to 4.243% due 2013 to 2022 [Member]		Dec. 31, 2012 Transition bonds 0.90% to 5.63% due 2013 to 2024 [Member]		Dec. 31, 2011 Transition bonds 0.90% to 5.63% due 2013 to 2024 [Member]		Dec. 31, 2012 Other [Member]		Dec. 31, 2011 Other [Member]		Dec. 31, 2012 Line of Credit [Member]	Dec. 31, 2011 Line of Credit [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Jan. 31, 2012 CenterPoint Energy Transition Bond Company IV, LLC [Member] tranches
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	$ 4,995			$ 4,262							$ 102	[1]	$ 102	[1]	$ 1,312	[1]	$ 1,762	[1]	$ 183	[2]	$ 183	[2]	$ 510		$ 556		$ 2,890		$ 1,659		$ (2)		$ 0
Long-term Debt, Current Maturities	897	[3]		353	[3]						0	[1],[3]	0	[1],[3]	450	[1],[3]	0	[1],[3]	0	[2],[3]	46	[2],[3]	46	[3]	45	[3]	401	[3]	262	[3]	0	[3]	0	[3]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum															2.25%				4.25%				1.833%				0.90%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum															6.95%				5.60%				4.243%				5.63%
Long-term Debt [Abstract]
Special purpose subsidiaries	5
Transition bonds issued to recover true-up costs			1,695
Line of Credit Facility [Abstract]
Letters of Credit Outstanding																																			4	4
Loans Outstanding																																			0	0
Size of Credit Facility																																			300	300
Percentage on limitation of debt to total capitalization under covenant (in hundredths)																																			65.00%
Number of tranches of transition bonds																																						3
Minimum interest rate on transition bonds			0.9012%
Maximum interest rate on transition bonds			3.0282%
Annual maturities of long-term debt [Abstract]
2013	897
2014	354
2015	372
2016	391
2017	538
Transition and system restoration bond principal repayments included in annual maturities [Abstract]
2013	447
2014	354
2015	372
2016	391
2017	411
Secured Debt											253				2,400
Replacement Fund Requirements	189
Sinking Fund Requirements	3
Debt Instrument, Face Amount						300	500
Debt Instrument, Interest Rate, Stated Percentage						2.25%	3.55%	5.75%	7.00%		9.15%
Extinguishment Of Debt Purchase Price Percentage Of Principal								107.332%	109.397%
Extinguishment of Debt, Amount								300	500
Number of general mortgage bond series called for redemption										2
Redemption Premium										$ 69
Line of Credit Facility, Interest Rate Description																																					Libor + .0125

[1] Debt issued as collateral is excluded from the financial statements because of the contingent nature of the obligation.

[2] These series of debt are secured by CenterPoint Houston’s general mortgage bonds.

[3] Includes amounts due or scheduled to be paid within one year of the date noted.