Regulatory Matters Regulatory Assets and Liabilities (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended						1 Months Ended
	Dec. 31, 2005	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2012	Dec. 31, 2004	Mar. 31, 2004	Jan. 31, 2012 CenterPoint Energy Transition Bond Company IV, LLC [Member] tranches	Dec. 31, 2012 Securitized regulatory asset [Member]	Dec. 31, 2011 Securitized regulatory asset [Member]	Dec. 31, 2012 True-up Settlement [Member]		Dec. 31, 2011 True-up Settlement [Member]		Dec. 31, 2012 Unrecognized equity return [Member]		Dec. 31, 2011 Unrecognized equity return [Member]		Dec. 31, 2012 Unamortized loss on reacquired debt [Member]	Dec. 31, 2011 Unamortized loss on reacquired debt [Member]	Dec. 31, 2012 Pension and postretirement-related regulatory asset [Member]		Dec. 31, 2011 Pension and postretirement-related regulatory asset [Member]		Dec. 31, 2012 Other long-term regulatory assets [Member]		Dec. 31, 2011 Other long-term regulatory assets [Member]		Dec. 31, 2012 Estimated removal costs [Member]	Dec. 31, 2011 Estimated removal costs [Member]	Dec. 31, 2012 Other long-term regulatory liabilities [Member]	Dec. 31, 2011 Other long-term regulatory liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets			$ 3,388,000,000	$ 3,726,000,000						$ 3,545,000,000	$ 2,289,000,000	$ 0	[1]	$ 1,684,000,000	[1]	$ (553,000,000)	[2]	$ (600,000,000)	[2]	$ 119,000,000	$ 56,000,000	$ 165,000,000	[3]	$ 177,000,000	[3]	$ 112,000,000	[4]	$ 120,000,000	[4]
Total regulatory liabilities			473,000,000	441,000,000																										346,000,000	339,000,000	127,000,000	102,000,000
Total regulatory assets and liabilities, net			2,915,000,000	3,285,000,000
Amount of allowed equity return on the true-up balance that has not been recognized			553,000,000
Amount of allowed equity return on the true-up balance that was recognized in the period			47,000,000	21,000,000	16,000,000
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided			14,000,000	16,000,000
Resolution of True-Up Appeal [Abstract]
Initial amount of true-up application								3,700,000,000
Amount awarded in final true-up order by the Texas Utility Commission							2,300,000,000
Net after-tax extraordinary gain (loss)	(947,000,000)	598,000,000	0	598,000,000	0
Additional amount allowed by district court on true-up appeal		1,695,000,000
Transition bonds issued to recover true-up costs						1,695,000,000
Number of tranches of transition bonds									3
Minimum interest rate on transition bonds						0.9012%
Maximum interest rate on transition bonds						3.0282%
Offering expenses									10,400,000
Extraordinary Item, Gain (Loss), Gross		921,000,000
Tax Effect of Extraordinary Item, Gain (Loss)		323,000,000
Return on true-up balance		352,000,000	0	352,000,000	0
Return on true-up balance after tax		229,000,000
Equity Return portion of Recoverable True-Up Balance pre-tax				405,000,000
Equity Return portion of Recoverable True-Up Balance after-tax				$ 263,000,000

[1] In accordance with a final order from the Public Utility Commission of Texas (Texas Utility Commission), the true-up settlement as of December 31, 2012 was not earning a return. The regulatory asset was securitized in January 2012 as a result of the issuance of the transition bonds described below in Note 4(b).

[2] As of December 31, 2012, CenterPoint Houston has not recognized an allowed equity return of $553 million because such return will be recognized as it is recovered in rates. During the years ended December 31, 2010, 2011 and 2012, CenterPoint Houston recognized approximately $16 million, $21 million and $47 million, respectively, of the allowed equity return.

[3] CenterPoint Houston’s actuarially determined pension and other postemployment expense in excess of the amount being recovered through rates is being deferred for rate making purposes and was addressed in its 2010 rate application pursuant to Texas law. Deferred pension and other postemployment expenses of $16 million and $14 million as of December 31, 2011 and 2012, respectively, were not earning a return.

[4] Other regulatory assets that are not earning a return were not material as of December 31, 2011 and 2012.