Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Interest, net of capitalized interest	$ 159	$ 148
Income tax payments, net	(4)	0
Accounts payable related to capital expenditures	166	200
ROU assets obtained in exchange for lease liabilities	1	14
Cash and cash equivalents	146		$ 147
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	167	247	167	$ 271
Prepaid Expenses and Other Current Assets [Member]
Restricted cash included in Prepaid expenses and other current assets	21		20
Houston Electric [Member]
Interest, net of capitalized interest	70	68
Income tax payments, net	0	0
Accounts payable related to capital expenditures	140	110
ROU assets obtained in exchange for lease liabilities	0	0
Cash and cash equivalents	143		139
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	159	215	154	235
Houston Electric [Member] | Bond Companies
Cash and cash equivalents	142		139
Houston Electric [Member] | Prepaid Expenses and Other Current Assets [Member]
Restricted cash included in Prepaid expenses and other current assets	16		15
CERC Corp [Member]
Interest, net of capitalized interest	21	35
Income tax payments, net	0	0
Accounts payable related to capital expenditures	56	66
ROU assets obtained in exchange for lease liabilities	0	5
Cash and cash equivalents	1		1
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	1	$ 1	1	$ 2
CERC Corp [Member] | Prepaid Expenses and Other Current Assets [Member]
Restricted cash included in Prepaid expenses and other current assets	$ 0		$ 0