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
Defined Benefit Plan Disclosure [Line Items]
Percentage of eligible earnings used to determine retirement benefits		5.00%		5.00%
Recognized pension expense				$ 44	$ 35	$ 26
Non Qualified Pension Plan Expense				$ 1	1	1
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				$ 15	14	$ 13
Components of net periodic costs [Abstract]
Service cost				1	1
Interest cost				$ 10	$ 13
Assumptions used to determine net periodic benefit (income) cost [Abstract]
Discount rate				4.35%	3.90%	4.75%
Expected long-term return on assets		4.75%	5.00%	5.00%	5.45%	6.00%
Change in Benefit Obligation
Accumulated benefit obligation, beginning of year				$ 283	$ 347
Service cost				1	1
Interest cost				10	13
Benefits paid				(20)	(17)
Participant contributions				3	3
Medicare drug reimbursement				1	1
Plan amendment (1)	[1]			(65)	(4)
Actuarial (gain) loss				4	(61)
Accumulated benefit obligation, end of year		$ 217	$ 283	217	283	$ 347
Change in Plan Assets
Plan assets, beginning of year				110	115
Benefits paid				(20)	(17)
Employer contributions				10	9
Participant contributions				3	3
Actual investment return				5	0
Plan amendment (2)	[2]			(20)	0
Plan assets, end of year		88	110	88	110	$ 115
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations		$ (148)	$ (192)	$ (148)	$ (192)
Actuarial Assumptions
Discount rate		4.15%	4.35%	4.15%	4.35%
Expected long-term return on assets		4.75%	5.00%	5.00%	5.45%	6.00%
Prescription drug 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%
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Effect of One Percentage Point Increase on Postretirement Benefit Obligation				$ 10
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation				10
Effect of One Percentage Point Increase on Total Service and Interest Cost				1
Effect of One Percentage Point Decrease on Total Service and Interest Cost				$ 0
Annualized individual discount rates based on time period, minimum				6 months
Annualized individual discount rates based on time period, maximum				99 years
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic costs [Abstract]
Service cost				$ 1	$ 1	$ 1
Interest cost				10	13	14
Expected return on plan assets				(5)	(6)	(6)
Amortization of transition obligation				0	0	4
Amortization of prior service credit				(4)	(2)	(2)
Amortization of loss				1	3	1
Curtailment				(4)	0	0
Net postretirement benefit cost (credit)				(1)	9	12
Change in Benefit Obligation
Service cost				1	1	1
Interest cost				10	13	$ 14
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations		$ (129)	$ (173)	(129)	(173)
Net liability, end of year		$ (129)	$ (173)	$ (129)	$ (173)
Maximum [Member]
Actuarial Assumptions
Healthcare cost trend rate assumed for the next year				10.65%	5.50%
Minimum [Member]
Actuarial Assumptions
Healthcare cost trend rate assumed for the next year				5.75%	6.00%
Health Care [Member]
Actuarial Assumptions
Year that the healthcare rate reaches the ultimate trend rate		2024	2024	2024	2024
Prescription Drug [Member]
Actuarial Assumptions
Year that the healthcare rate reaches the ultimate trend rate		2024	2024	2024	2024
CenterPoint Energy [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Maximum Limit Of Account Balance In Company Stock, Percentage				25.00%
Number Of Shares In Common Stock Held By Savings Plan		14,216,986		14,216,986
Percentage of investment in common stocks		17.00%		17.00%

[1] The Postretirement plan was amended during 2016 to change retiree medical coverage, effective January 1, 2017, as follows: (i) members of the IBEW Local Union 66 who retire on or after January 1, 2017, and their dependents, will receive any retiree medical and prescription drug coverage exclusively through the NECA/IBEW Family Medical Care Plan pursuant to the terms of the renegotiated collective bargaining agreement entered into in May 2016; and (ii) Medicare eligible post-65 retirees will receive coverage through a Medicare Advantage Program, an insured benefit, in lieu of the previous self-insured benefit. These changes resulted in a reduction in our Postretirement Plan liability of $65 million as of December 31, 2016.

[2] In May 2016, Houston Electric entered into a renegotiated collective bargaining agreement with the IBEW Local Union 66 and amended the Houston Electric Union Postretirement Trust. The amendment resulted in a split of the trust into two segregated and restricted accounts, one holds assets for the benefit of current, retired on or before December 31, 2016, union retirees and one holds assets for the benefit of post-2016 union retirees who are now covered exclusively by the NECA/IBEW Family Medical Care Plan. Accordingly, $20 million was transferred to the account for post-2016 union retirees.