Regulatory Matters Regulatory Assets and Regulatory Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets	$ 633	$ 788
Unrecognized equity return (2)	(150)	(168)
Unamortized loss on reacquired debt (3)	57	62
Non-current regulatory assets	2,094	2,117
Total regulatory assets	2,127	2,129
Non-current regulatory liabilities	3,448	3,474
Total regulatory liabilities	3,520	3,521
Total regulatory assets and liabilities, net	(1,393)	(1,392)
Amount of allowed equity return on the true-up balance that was recognized in the period	31	45	$ 74
Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	33	12
Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (6)	72	47
Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	1,484	1,582
Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	1,470	1,429
Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	494	463
Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	591	637
Hurricane Harvey
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	59
Hurricane Laura
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	36
Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 25	30
Weighted average recovery period	4 years
Relief Program Incremental Costs (COVID-19)
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 25
Asset Retirement Obligation Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	135	131
Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	518	422
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided	$ 165	147
Remaining weighted average period for which no return on investment during recovery period is provided	14 years
Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets		68
Houston Electric [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets	$ 633	788
Unrecognized equity return (2)	(137)	(168)
Unamortized loss on reacquired debt (3)	55	62
Non-current regulatory assets	848	915
Total regulatory assets	848	915
Non-current regulatory liabilities	1,252	1,288
Total regulatory liabilities	1,295	1,288
Total regulatory assets and liabilities, net	(447)	(373)
Amount of allowed equity return on the true-up balance that was recognized in the period	31	45	$ 74
Houston Electric [Member] | Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	0	0
Houston Electric [Member] | Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (6)	43	0
Houston Electric [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	764	821
Houston Electric [Member] | Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	231	244
Houston Electric [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	257	223
Houston Electric [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	31	34
Houston Electric [Member] | Hurricane Harvey
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	55
Houston Electric [Member] | Hurricane Laura
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	36
Houston Electric [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 20	23
Weighted average recovery period	5 years
Houston Electric [Member] | Relief Program Incremental Costs (COVID-19)
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 5
Houston Electric [Member] | Asset Retirement Obligation Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	26	26
Houston Electric [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	41	29
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided	$ 83	57
Remaining weighted average period for which no return on investment during recovery period is provided	11 years
Houston Electric [Member] | Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets		64
CERC Corp [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Securitized regulatory assets	$ 0	0
Unrecognized equity return (2)	(13)	0
Unamortized loss on reacquired debt (3)	0	0
Non-current regulatory assets	220	191
Total regulatory assets	253	203
Non-current regulatory liabilities	1,226	1,219
Total regulatory liabilities	1,255	1,266
Total regulatory assets and liabilities, net	(1,002)	(1,063)
CERC Corp [Member] | Prepaid Expenses and Other Current Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory assets (1)	33	12
CERC Corp [Member] | Other Current Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities (6)	29	47
CERC Corp [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	421	442
CERC Corp [Member] | Removal Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	656	637
CERC Corp [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory liabilities	149	140
CERC Corp [Member] | Pension and Other Postretirement Plans Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	21	22
CERC Corp [Member] | Hurricane Harvey
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	4
CERC Corp [Member] | Hurricane Laura
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	0
CERC Corp [Member] | Amounts related to TCJA [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 5	7
Weighted average recovery period	3 years
CERC Corp [Member] | Relief Program Incremental Costs (COVID-19)
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	$ 17
CERC Corp [Member] | Asset Retirement Obligation Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	107	94
CERC Corp [Member] | Other Regulatory Assets (Liabilities) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets	35	16
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided	$ 44	48
Remaining weighted average period for which no return on investment during recovery period is provided	27 years
CERC Corp [Member] | Hurricane Harvey [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-current regulatory assets		$ 4