Regulatory Matters (Details) - USD ($) $ in Millions	Dec. 31, 2020	Apr. 13, 2020
Natural Gas [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Uncollectible Receivables, Regulatory Asset	$ 22
CERC Corp [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Uncollectible Receivables, Regulatory Asset	19
Public Utility Commission of Texas [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 ERP Regulatory Liability	6
ERCOT Loan, COVID-19 ERP		$ 5
Public Utility Commission of Texas [Member] | Houston Electric [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 ERP Regulatory Liability	$ 6
ERCOT Loan, COVID-19 ERP		$ 5