Commitments and Contingencies (Details) (USD $)	9 Months Ended					9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 CenterPoint Energy [Member]	Sep. 30, 2013 CERC Corp [Member]	Sep. 30, 2013 Midstream Partnership [Member]	May 01, 2013 Midstream Partnership [Member]	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Minimum [Member]
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
2013	$ 143,000,000
2014	449,000,000
2015	382,000,000
2016	309,000,000
2017	250,000,000
After 2017	366,000,000
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)	1
Site Contingency Completed Remediation	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
Accrual for Environmental Loss Contingencies	13,000,000
Maximum estimated remediation costs for the Minnesota sites						41,000,000	6,000,000
Minimum years of remediation for the Minnesota sites (in years)						50	30
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	6,100,000
Approximate amount of undiscounted maximum potential guarantee obligation	62,000,000		53,200,000
Guarantor Obligations, Current Amount			1,000,000	1,050,000,000	1,050,000,000
Guarantee Obligations Maximum Amount Upon Completion Of Gathering Systems		$ 100,000,000