Commitments and Contingencies (Details) (USD $)	6 Months Ended
	Jun. 30, 2012
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
2012	$ 185,000,000
2013	428,000,000
2014	339,000,000
2015	210,000,000
2016	148,000,000
After 2016	251,000,000
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Recovery of compensatory damages sought by plaintiffs	in excess of $1 billion
Approximate number of gas market manipulatioin lawsuits naming CenterPoint Energy and/or Reliant Energy (in number of lawsuits)	30
Number of gas market manipulation lawsuits pending for CenterPoint and its affiliates (in number of lawsuits)	2
Number of gas market mismeasurement lawsuits pending for CenterPoint and its affiliates (in number of lawsuits)	2
Approximate number of pipeline companies named in the mismeasurement lawsuits (in number of companies)	245
Number of gas measurement lawsuits seeking class certification and has four amendments (in number of cases)	1
Number of times gas measurement lawsuit was amended (in number of amendments)	4
Number of years the plaintiffs claim the defendants have engaged in the systematic mismeasurement of natural gas (in years)	25
Number of CenterPoint subsidiaries dismissed from the claims of the plaintiff (in number of claims)	2
Number of sites where remediation is complete, other than ongoing operations (in number of sites)	2
Number of remaining sites in the Minnesota service territory (in number of sites)	5
Number of remaining sites in the Minnesota service territory where the company believes it has no liability (in number of sites)	2
Amount accrued for remediation of Minnesota sites	13,000,000
Minimum estimated remediation costs for the Minnesota sites	6,000,000
Maximum estimated remediation costs for the Minnesota sites	41,000,000
Minimum years of remediation for the Minnesota sites (in years)	30
Maximum estimated remediation for the Minnesota sites (in years)	50
Annual amount included in rates to fund normal on-going remediation costs	285,000
Amount collected from insurance companies to be used for future environmental remediation	5,700,000
Approximate amount of undiscounted maximum potential demand charges under the transportation contracts	82,000,000
Approximate amount of collateral posted as security on transportaion contracts	28,000,000
Long-Term Gas Gathering and Treating Agreements [Member]
Schedule of Capital Expansion Projects [Abstract]
Estimated Total Capital Expenditures For Expansion	$ 440,000,000
Total Capacity Of System After Potential Additional Expansion	1.3