Regulatory Accounting (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets		$ 1,059	$ 1,590
Unrecognized equity return (2)	[1]	(213)	(287)
Unamortized loss on reacquired debt		68	75
Non-current regulatory assets		1,967	2,347
Total regulatory assets		2,044	2,477
Non-current regulatory liabilities		2,525	2,464
Total regulatory liabilities		2,563	2,488
Total regulatory assets and liabilities, net		(519)	(11)
Amount of allowed equity return on the true-up balance that was recognized in the period		74	42	$ 64
Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	[2]	77	130
Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (7)	[3]	38	24
Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	[4]	1,323	1,354
Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		886	878
Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		316	232
Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[5]	725	646
Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[4]	33	48
Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[6]	227	211
Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[7]	68	64
Natural Gas Distribution [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided		4	7
Electric Transmission & Distribution [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided		33	31
Houston Electric [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets		1,059	1,590
Unrecognized equity return (2)	[1]	(213)	(287)
Unamortized loss on reacquired debt		68	75
Non-current regulatory assets		1,124	1,570
Total regulatory assets		1,124	1,570
Non-current regulatory liabilities		1,298	1,263
Total regulatory liabilities		1,315	1,285
Total regulatory assets and liabilities, net		(191)	285
Amount of allowed equity return on the true-up balance that was recognized in the period		74	42	$ 64
Houston Electric [Member] | Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	[2]	0	0
Houston Electric [Member] | Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (7)	[3]	17	22
Houston Electric [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	[4]	847	862
Houston Electric [Member] | Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		269	285
Houston Electric [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		182	116
Houston Electric [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[5]	33	31
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided		33	31
Houston Electric [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[4]	23	33
Houston Electric [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[6]	90	70
Houston Electric [Member] | Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[7]	64	58
CERC Corp [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets		0	0
Unrecognized equity return (2)	[1]	0	0
Unamortized loss on reacquired debt		0	0
Non-current regulatory assets		181	181
Total regulatory assets		258	311
Non-current regulatory liabilities		1,227	1,201
Total regulatory liabilities		1,248	1,203
Total regulatory assets and liabilities, net		(990)	(892)
CERC Corp [Member] | Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	[2]	77	130
CERC Corp [Member] | Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (7)	[3]	21	2
CERC Corp [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	[4]	476	492
CERC Corp [Member] | Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		617	593
CERC Corp [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities		134	116
CERC Corp [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[5]	30	20
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided		4	7
CERC Corp [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[4]	10	15
CERC Corp [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[6]	137	140
CERC Corp [Member] | Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	[7]	$ 4	$ 6

[1] The unrecognized equity return will be recognized as it is recovered in rates through 2024. During the years ended December 31, 2018, 2017 and 2016, Houston Electric recognized approximately $74 million, $42 million and $64 million, respectively, of the allowed equity return. The timing of Houston Electric’s recognition of the equity return will vary each period based on amounts actually collected during the period. The actual amounts recognized are adjusted at least annually to correct any over-collections or under-collections during the preceding 12 months.

[2] Current regulatory assets are included in Prepaid expenses and other current assets in the Registrants’ respective Consolidated Balance Sheets.

[3] Current regulatory liabilities are included in Other current liabilities in each of the Registrants’ respective Consolidated Balance Sheets.

[4] The EDIT and deferred revenues will be recovered or refunded to customers as required by tax and regulatory authorities. See Note 15 for additional information.

[5] Includes a portion of Houston Electric’s and CERC’s NGD’s actuarially determined pension and other postemployment expense in excess of the amount being recovered through rates that is being deferred for rate making purposes, of which $33 million and $4 million as of December 31, 2018, respectively, and $31 million and $7 million as of December 31, 2017, respectively, were not earning a return.

[6] Other long-term regulatory assets that are not earning a return were not material as of December 31, 2018 and 2017.

[7] The Registrants suffered damage as a result of Hurricane Harvey, a major storm classified as a Category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale, that first struck the Texas coast on Friday, August 25, 2017 and remained over the Houston area for the next several days. The unprecedented flooding from torrential amounts of rainfall accompanying the storm caused significant damage to or destruction of residences and businesses served by the Registrants. The Registrants deferred the uninsured storm restoration costs as management believed it was probable that such costs will be recovered through traditional rate adjustment mechanisms for capital costs and through the next base rate proceeding for operation and maintenance expenses. As a result, storm restoration costs did not materially affect the Registrants’ reported net income for 2017. The Registrants are not earning a return on Hurricane Harvey restoration costs.