Employee Benefit Plans Pension and Postretirement Benefits (Details) - USD ($) $ in Millions				12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Pension and Savings Plan
Percentage of eligible earnings used to determine retirement benefits							5.00%
Pension Expense				$ 35	$ 24	$ 27
Non Qualified Pension Plan Benefit Expense				$ 3	2	2
Maximum Percentage Of Employee Compensation Eligible For Contribution To Savings Plan				50.00%
Description Of Company Match Under Savings Plan				100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay				6.00%
Defined Contribution Plan, Cost Recognized				$ 16	14	20
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations							$ (104)	$ (89)
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Tax benefit (expense)				4	(6)	1
Net current period other comprehensive income (loss)				(6)	8	(4)
Effect of a one-percentage point change in assumed healthcare cost trend rates
Deferred Compensation Arrangement with Individual, Compensation Expense				1	1	1
Other Pension Plan, Postretirement or Supplemental Plans [Member]
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Other comprehensive income (loss) before reclassifications (1)	[1]			(10)	13
Actuarial gains (2)	[2]			0	1
Tax benefit (expense)				4	(6)
Net current period other comprehensive income (loss)				(6)	8
Ending Balance		$ 3	$ 9	3	9	1
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss							5	3
Unrecognized prior service cost (credit)							7	(1)
Total recognized in accumulated other comprehensive loss							12	2
Less: deferred tax benefit (1)	[3]						(15)	(11)
Net amount recognized in accumulated other comprehensive income		$ (3)	$ (9)	(3)	(9)	(1)	(3)	(9)
Effect of a one-percentage point change in assumed healthcare cost trend rates
Defined Benefit Plan, Accumulated Other Comprehensive Income Net Gains (Losses), after Tax							3	9
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost — benefits earned during the period				1	1	1
Interest cost on accumulated benefit obligation				4	5	5
Expected return on plan assets				(1)	(1)	(1)
Amortization of prior service cost				0	1	1
Amortization of net loss				1	1	1
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	[4]			(1)	0	0
Net postretirement benefit cost				$ 4	$ 7	$ 7
Assumptions used to determine net postretirement benefit costs
Discount rate				4.35%	3.90%	4.75%
Expected return on plan assets		3.60%	3.95%	3.95%	4.05%	3.10%
Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation, beginning of year				$ 101	$ 126
Service cost — benefits earned during the period				1	1	$ 1
Interest cost on accumulated benefit obligation				4	5	5
Benefits paid				(13)	(12)
Participant contributions				5	4
Medicare reimbursement				1	1
Plan amendment (1)	[5]			10	(5)
Actuarial (gain) loss				6	(19)
Accumulated benefit obligation, end of year		$ 115	$ 101	115	101	126
Change in Plan Assets [Roll Forward]
Plan assets, beginning of year				25	26
Benefits paid				(13)	(12)
Employer contributions				7	7
Participant contributions				5	4
Actual investment return				1	0
Plan assets, end of year		$ 25	$ 25	$ 25	$ 25	$ 26
Amounts Recognized in Balance Sheets
Current liabilities-other							(4)	(6)
Other liabilities-benefit obligations							(86)	(70)
Net liability, end of year							$ (90)	$ (76)
Discount rate							4.15%	4.35%
Expected return on plan assets		3.60%	3.95%	3.95%	4.05%	3.10%
Prescription cost trend rate assumed for the next year				10.75%	11.00%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)				4.50%	5.00%
Annualized individual discount rates based on time period, minimum				6 months
Annualized individual discount rates based on time period, maximum				99 years
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss				$ 2
Amortization of prior service cost				8
Total recognized in other comprehensive loss				10
Total expense (benefit) recognized in net periodic cost and other comprehensive income				(14)
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit)				1
Effect of a one-percentage point change in assumed healthcare cost trend rates
Effect of One Percentage Point Increase on Postretirement Benefit Obligation				4
Effect of One Percentage Point Increase on Total of Service and Interest Cost				0
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation				4
Effect of One Percentage Point Decrease on Total of Service and Interest Cost				$ 0
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Healthcare cost trend rate assumed for the next year				5.75%	6.00%
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Healthcare cost trend rate assumed for the next year				10.65%	5.50%
Health Care [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Year that the healthcare rate reaches the ultimate trend rate							2024	2024
Prescription Drug [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Year that the healthcare rate reaches the ultimate trend rate							2024	2024
Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Liability, Classified, Noncurrent							$ 3	$ 3
Effect of a one-percentage point change in assumed healthcare cost trend rates
Postemployment Benefits Liability, Noncurrent							$ 14	$ 14
CenterPoint Energy [Member] | Common Stock [Member]
Pension and Savings Plan
Defined contribution plan, Maximum percentage allowed in company stock				25.00%
Number Of Shares In Common Stock Held By Savings Plan							14,216,986
Percentage of investment in common stocks							17.00%

[1] Total other comprehensive income (loss) related to the remeasurement of pension, postretirement and other postemployment plans.

[2] These accumulated other comprehensive components are included in the computation of net periodic cost.

[3] CERC’s postretirement benefit obligation is reduced by the impact of previously non-taxable government subsidies under the Medicare Prescription Drug Act. Because the subsidies were non-taxable, the temporary difference used in measuring the deferred tax impact was determined on the unrecognized losses excluding such subsidies.

[4] Effective January 1, 2017, a change in retiree medical coverage for Medicare eligible post-65 retirees from self-insured to a Medicare Advantage Program, an insured benefit, was implemented. A curtailment gain was recognized in October 2016 related to this implementation.

[5] The postretirement plan was amended in 2016 to change the retiree medical coverage for Medicare eligible post-65 retirees from self-insured to a Medicare Advantage Program, an insured benefit which became effective January 1, 2017.