Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost (income)	$ 8	$ 11
Total contributions expected in current year	61
Total contributions to the plans during the period	8
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost (income)	1	1
Total contributions expected in current year	9
Total contributions to the plans during the period	3
Operation and maintenance expense [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	10	10
Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	1	0
Other, net [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	15	19
Expected return on plan assets (2)	(26)	(28)
Amortization of net loss (2)	9	10
Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	2	3
Expected return on plan assets (2)	(1)	(1)
Amortization of prior service cost (2)	(1)	(1)
Houston Electric [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions expected in current year	0
Total contributions to the plans during the period	0
Houston Electric [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost (income)	(1)	(1)
Total contributions expected in current year	1
Total contributions to the plans during the period	0
Houston Electric [Member] | Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	0	0
Houston Electric [Member] | Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	1	1
Expected return on plan assets (2)	(1)	(1)
Amortization of prior service cost (2)	(1)	(1)
CERC Corp [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions expected in current year	0
Total contributions to the plans during the period	0
CERC Corp [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost (income)	1	1
Total contributions expected in current year	3
Total contributions to the plans during the period	1
CERC Corp [Member] | Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	0	0
CERC Corp [Member] | Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	1	1
Expected return on plan assets (2)	0	0
Amortization of prior service cost (2)	$ 0	$ 0