Stock-Based Incentive Compensation Plans and Employee Benefit Plans Change in Control Agreements and Other Employee Matters (Details)	12 Months Ended
	Dec. 31, 2018 salary_severance_benefits
Concentration Risk [Line Items]
Maximum Number Of Times Annual Salary Included In Severance Benefits	3
Workforce Subject to Collective Bargaining Arrangements Expiring in May 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	18.00%
Workforce Subject to Collective Bargaining Arrangements Expiring in March and May 2021 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	3.00%
Workforce Subject to Collective Bargaining Arrangements Expiring in April 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	6.00%
Workforce Subject to Collective Bargaining Arrangements Expiring in December 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	3.00%
Workforce Subject to Collective Bargaining Arrangements Expiring in June and July 2022 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	5.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	35.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in May 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	51.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in March and May 2021 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in April 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in December 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in June and July 2022 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%
Houston Electric [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	51.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in May 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in March and May 2021 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	3.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in April 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	12.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in December 2020 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	7.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring in June and July 2022 [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	11.00%
CERC Corp [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] | Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	33.00%