Regulatory Accounting (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Securitized regulatory assets		$ 977		$ 1,059
Unrecognized equity return (2)	[1]	(202)		(213)
Unamortized loss on reacquired debt		66		68
Regulatory assets		2,229		1,967
Total regulatory assets		2,265		2,044
Regulatory liabilities		3,449		2,525
Total regulatory liabilities		3,516		2,563
Total regulatory assets and liabilities, net		(1,251)		(519)
Amount of allowed equity return on the true-up balance that was recognized in the period		11	$ 21
Houston Electric [Member]
Securitized regulatory assets		977		1,059
Unrecognized equity return (2)	[1]	(202)		(213)
Unamortized loss on reacquired debt		66		68
Regulatory assets		1,056		1,124
Total regulatory assets		1,056		1,124
Regulatory liabilities		1,272		1,298
Total regulatory liabilities		1,283		1,315
Total regulatory assets and liabilities, net		(227)		(191)
Amount of allowed equity return on the true-up balance that was recognized in the period		11	$ 21
CERC Corp [Member]
Securitized regulatory assets		0		0
Unrecognized equity return (2)		0		0
Unamortized loss on reacquired debt		0		0
Regulatory assets		180		181
Total regulatory assets		216		258
Regulatory liabilities		1,233		1,227
Total regulatory liabilities		1,271		1,248
Total regulatory assets and liabilities, net		(1,055)		(990)
Hurricane Harvey [Member]
Regulatory assets		68		68
Hurricane Harvey [Member] | Houston Electric [Member]
Regulatory assets		64		64
Hurricane Harvey [Member] | CERC Corp [Member]
Regulatory assets		4		4
Prepaid expenses and other current assets [Member]
Current regulatory assets (1)	[2]	36		77
Prepaid expenses and other current assets [Member] | Houston Electric [Member]
Current regulatory assets (1)	[2]	0		0
Prepaid expenses and other current assets [Member] | CERC Corp [Member]
Current regulatory assets (1)	[2]	36		77
Other current liabilities [Member]
Current regulatory liabilities (7)	[3]	67		38
Other current liabilities [Member] | Houston Electric [Member]
Current regulatory liabilities (7)	[3]	11		17
Other current liabilities [Member] | CERC Corp [Member]
Current regulatory liabilities (7)	[3]	38		21
Pension and Other Postretirement Plans Costs [Member]
Regulatory assets	[4]	711		725
Pension and Other Postretirement Plans Costs [Member] | Houston Electric [Member]
Regulatory assets	[4]	34		33
Other regulatory assets-not earning a return (5)		34		33
Pension and Other Postretirement Plans Costs [Member] | CERC Corp [Member]
Regulatory assets	[4]	29		30
Amounts related to TCJA [Member]
Regulatory assets	[5]	29		33
Amounts related to TCJA [Member] | Houston Electric [Member]
Regulatory assets	[5]	23		23
Amounts related to TCJA [Member] | CERC Corp [Member]
Regulatory assets	[5]	6		10
Other Regulatory Assets (Liabilities) [Member]
Regulatory assets		466		146
Other regulatory assets-not earning a return (5)	[6]	114		81
Other Regulatory Assets (Liabilities) [Member] | Houston Electric [Member]
Regulatory assets		37		35
Other regulatory assets-not earning a return (5)	[6]	57		55
Other Regulatory Assets (Liabilities) [Member] | CERC Corp [Member]
Regulatory assets		115		111
Other regulatory assets-not earning a return (5)	[6]	26		26
Amounts related to TCJA [Member]
Regulatory liabilities	[5]	1,628		1,323
Amounts related to TCJA [Member] | Houston Electric [Member]
Regulatory liabilities	[5]	841		847
Amounts related to TCJA [Member] | CERC Corp [Member]
Regulatory liabilities	[5]	456		476
Removal Costs [Member]
Regulatory liabilities		1,404		886
Removal Costs [Member] | Houston Electric [Member]
Regulatory liabilities		271		269
Removal Costs [Member] | CERC Corp [Member]
Regulatory liabilities		624		617
Other Regulatory Assets (Liabilities) [Member]
Regulatory liabilities		417		316
Other Regulatory Assets (Liabilities) [Member] | Houston Electric [Member]
Regulatory liabilities		160		182
Other Regulatory Assets (Liabilities) [Member] | CERC Corp [Member]
Regulatory liabilities		153		134
Houston Electric T&D [Member] | Pension and Other Postretirement Plans Costs [Member]
Other regulatory assets-not earning a return (5)		34		33
Natural Gas Distribution [Member] | Pension and Other Postretirement Plans Costs [Member]
Other regulatory assets-not earning a return (5)		3		4
Natural Gas Distribution [Member] | Pension and Other Postretirement Plans Costs [Member] | CERC Corp [Member]
Other regulatory assets-not earning a return (5)		$ 3		$ 4

[1] The unrecognized equity return will be recognized as it is recovered in rates through 2024. During the three months ended March 31, 2019 and 2018, Houston Electric recognized approximately $11 million and $21 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 Condensed Consolidated Balance Sheets.

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

[4] 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 $34 million and $3 million as of March 31, 2019, respectively, and $33 million and $4 million as of December 31, 2018, respectively, were not earning a return.

[5] The EDIT and deferred revenues will be recovered or refunded to customers as required by tax and regulatory authorities.

[6] Regulatory assets acquired in the Merger and not earning a return were recorded at fair value as of the Merger Date. Such fair value adjustments are recognized over time until the regulatory asset is recovered.