Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Interest, net of capitalized interest	$ 167	$ 182
Income taxes, net	88	11
Accounts payable related to capital expenditures	133	106
Cash and cash equivalents	328		$ 260
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	366	280	296	$ 381
Prepaid expenses and other current assets [Member]
Restricted cash	37		35
Other [Member]
Restricted cash	1		1
Houston Electric [Member]
Interest, net of capitalized interest	90	94
Income taxes, net	120	76
Accounts payable related to capital expenditures	75	75
Cash and cash equivalents	253		238
Total cash, cash equivalents and restricted cash shown in Condensed Statements of Consolidated Cash Flows	291	277	274	381
Houston Electric [Member] | Prepaid expenses and other current assets [Member]
Restricted cash	37		35
Houston Electric [Member] | Other [Member]
Restricted cash	1		1
CERC Corp [Member]
Interest, net of capitalized interest	50	56
Income taxes, net	3	3
Accounts payable related to capital expenditures	69	44
Cash and cash equivalents	$ 1	$ 1	$ 12	$ 1