Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Provision for doubtful accounts		$ 16	$ 14	$ 7
Interest Expense [Member]
Significant Accounting Policies [Line Items]
Interest and AFUDC debt (1)	[1]	8	9	8
Other Income (Expense) [Member]
Significant Accounting Policies [Line Items]
AFUDC equity (2)	[2]	12	11	7
Houston Electric [Member]
Significant Accounting Policies [Line Items]
Provision for doubtful accounts		0	1	0
Houston Electric [Member] | Interest Expense [Member]
Significant Accounting Policies [Line Items]
Interest and AFUDC debt (1)	[1]	6	6	6
Houston Electric [Member] | Other Income (Expense) [Member]
Significant Accounting Policies [Line Items]
AFUDC equity (2)	[2]	10	10	6
CERC Corp [Member]
Significant Accounting Policies [Line Items]
Provision for doubtful accounts		16	13	7
CERC Corp [Member] | Interest Expense [Member]
Significant Accounting Policies [Line Items]
Interest and AFUDC debt (1)	[1]	2	2	2
CERC Corp [Member] | Other Income (Expense) [Member]
Significant Accounting Policies [Line Items]
AFUDC equity (2)	[2]	2	1	1
Accounting Standards Update 2016-02 [Member]
Significant Accounting Policies [Line Items]
Amount of right-of-use assets and liabilities to recognize on the statement of financial position upon adoption of ASU 2016-02		30
Accounting Standards Update 2016-02 [Member] | Houston Electric [Member]
Significant Accounting Policies [Line Items]
Amount of right-of-use assets and liabilities to recognize on the statement of financial position upon adoption of ASU 2016-02		1
Accounting Standards Update 2016-02 [Member] | CERC Corp [Member]
Significant Accounting Policies [Line Items]
Amount of right-of-use assets and liabilities to recognize on the statement of financial position upon adoption of ASU 2016-02		28
Accounting Standards Update 2016-15 [Member]
Significant Accounting Policies [Line Items]
Effect of change on cash flow activities due to adoption of new ASU		2	4	8
Accounting Standards Update 2016-15 [Member] | Houston Electric [Member]
Significant Accounting Policies [Line Items]
Effect of change on cash flow activities due to adoption of new ASU		2	4	8
Accounting Standards Update 2016-18 [Member]
Significant Accounting Policies [Line Items]
Effect of change on cash flow activities due to adoption of new ASU		(11)	(4)	5
Accounting Standards Update 2016-18 [Member] | Houston Electric [Member]
Significant Accounting Policies [Line Items]
Effect of change on cash flow activities due to adoption of new ASU			(4)	5
Accounting Standards Update 2016-18 [Member] | CERC Corp [Member]
Significant Accounting Policies [Line Items]
Effect of change on cash flow activities due to adoption of new ASU		(11)
Accounting Standards Update 2017-07 [Member] | Operating Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		47	64	64
Accounting Standards Update 2017-07 [Member] | Other Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		(47)	(64)	(64)
Accounting Standards Update 2017-07 [Member] | Houston Electric [Member] | Operating Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		21	26	25
Accounting Standards Update 2017-07 [Member] | Houston Electric [Member] | Other Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		(21)	(26)	(25)
Accounting Standards Update 2017-07 [Member] | CERC Corp [Member] | Operating Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		11	23	23
Accounting Standards Update 2017-07 [Member] | CERC Corp [Member] | Other Income [Member]
Significant Accounting Policies [Line Items]
Increase to operating income and corresponding (decrease) to other income from the adoption of ASU 2017-07		(11)	(23)	$ (23)
Accounting Standards Update 2018-02 [Member]
Significant Accounting Policies [Line Items]
Tax (benefit) expense reclassification adjustment related to adoption of ASU 2018-02		(15)	0
Accounting Standards Update 2018-02 [Member] | Houston Electric [Member]
Significant Accounting Policies [Line Items]
Tax (benefit) expense reclassification adjustment related to adoption of ASU 2018-02		0	0
Accounting Standards Update 2018-02 [Member] | CERC Corp [Member]
Significant Accounting Policies [Line Items]
Tax (benefit) expense reclassification adjustment related to adoption of ASU 2018-02		$ (1)	$ 0

[1] Included in Interest and other finance charges on the Registrants’ respective Statements of Consolidated Income.

[2] Included in Other Income (Expense) on the Registrants’ respective Statements of Consolidated Income.