Employee Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan, Change in Accumulated Comprehensive Loss [Roll Forward]
Beginning Balance		$ (65)	$ (71)	$ (66)	$ (72)
Amounts reclassified from accumulated other comprehensive loss:
Prior service cost (1)	[1]	1	1	1	1
Actuarial losses (1)	[1]	1	1	3	3
Tax expense		0	(1)	(1)	(2)
Net current period other comprehensive income		2	1	3	2
Ending Balance		(63)	(70)	(63)	(70)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost		15	25	30	48
Total contributions expected in current year		67		67
Total contributions to the plans during the period		2		64
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost		2	2	3	4
Total contributions expected in current year		16		16
Total contributions to the plans during the period		3		7
Operation and maintenance expense [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	[2]	9	9	18	18
Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	[2]	1	1	1	1
Other, net [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	[3]	19	22	39	44
Expected return on plan assets (2)	[3]	(26)	(24)	(53)	(48)
Amortization of prior service cost (credit) (2)	[3]	2	3	4	5
Amortization of net loss (2)	[3]	11	15	22	29
Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	[3]	4	4	7	8
Expected return on plan assets (2)	[3]	(2)	(2)	(3)	(3)
Amortization of prior service cost (credit) (2)	[3]	(1)	(1)	(2)	(2)
Houston Electric [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost		(1)	0	(1)	0
Total contributions expected in current year		10		10
Total contributions to the plans during the period		2		4
Houston Electric [Member] | Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	[2]	0	0	0	0
Houston Electric [Member] | Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	[3]	2	2	4	4
Expected return on plan assets (2)	[3]	(1)	(1)	(2)	(2)
Amortization of prior service cost (credit) (2)	[3]	(2)	(1)	(3)	(2)
CERC Corp [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic cost		1	2	2	3
Total contributions expected in current year		5		5
Total contributions to the plans during the period		1		2
CERC Corp [Member] | Operation and maintenance expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	[2]	0	0	0	0
CERC Corp [Member] | Other, net [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost (2)	[3]	1	1	2	2
Expected return on plan assets (2)	[3]	(1)	0	(1)	0
Amortization of prior service cost (credit) (2)	[3]	$ 1	$ 1	$ 1	$ 1

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

[2] Included in Operation and maintenance expense in the Registrants’ Condensed Statements of Consolidated Income.

[3] Included in Other, net in the Registrants’ Condensed Statements of Consolidated Income.