Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Interest, net of capitalized interest	$ 154	$ 116
Income taxes (refunds), net	(4)	(4)
Accounts payable related to capital expenditures	166	102
ROU assets obtained in exchange for lease liabilities	29	0
Cash and cash equivalents	255		$ 4,231
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	355	257	4,278	$ 296
Prepaid expenses and other current assets [Member]
Restricted cash	99		46
Other [Member]
Restricted cash	1		1
Houston Electric [Member]
Interest, net of capitalized interest	86	61
Income taxes (refunds), net	0	16
Accounts payable related to capital expenditures	98	78
ROU assets obtained in exchange for lease liabilities	1	0
Cash and cash equivalents	243		335
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	277	229	370	274
Houston Electric [Member] | Prepaid expenses and other current assets [Member]
Restricted cash	33		34
Houston Electric [Member] | Other [Member]
Restricted cash	1		1
CERC Corp [Member]
Interest, net of capitalized interest	35	39
Income taxes (refunds), net	0	0
Accounts payable related to capital expenditures	49	39
ROU assets obtained in exchange for lease liabilities	26	0
Cash and cash equivalents	1		14
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	12	$ 27	25	$ 12
CERC Corp [Member] | Prepaid expenses and other current assets [Member]
Restricted cash	11		11
CERC Corp [Member] | Other [Member]
Restricted cash	$ 0		$ 0