Equity (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Class of Stock [Line Items]
Preferred stock dividend requirement		$ 29	$ 0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(108)	(68)
Actuarial losses	[1]	2	2
Reclassification of deferred loss from cash flow hedges realized in net income		1	0
Tax expense		(1)	(2)
Net current period other comprehensive income (loss)		1	5
Ending Balance		$ (107)	$ (63)
Common Stock [Member]
Class of Stock [Line Items]
Dividends declared per share		$ 0.0000	$ 0.0000
Dividends paid per share		$ 0.2875	$ 0.2775
Total dividends paid		$ 144	$ 120
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 0.0000
Dividends paid per share		$ 32.1563
Total dividends paid		$ 26
Preferred stock dividend requirement		$ 12	0
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 0.0000
Dividends paid per share		$ 17.5000
Total dividends paid		$ 17
Preferred stock dividend requirement		17	0
Houston Electric [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(14)	0
Actuarial losses	[1]	0	0
Reclassification of deferred loss from cash flow hedges realized in net income		0	0
Tax expense		0	(1)
Net current period other comprehensive income (loss)		(1)	4
Ending Balance		(15)	4
CERC Corp [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		5	6
Actuarial losses	[1]	0	0
Reclassification of deferred loss from cash flow hedges realized in net income		0	0
Tax expense		0	0
Net current period other comprehensive income (loss)		0	0
Ending Balance		5	6
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	(1)	5
Interest Rate Contract [Member] | Houston Electric [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	(1)	5
Interest Rate Contract [Member] | CERC Corp [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	$ 0	$ 0
First Quarter 2019 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date		Dec. 12, 2018
Record Date		Feb. 21, 2019
Payment Date		Mar. 14, 2019
Dividends paid per share		$ 0.2875
Total dividends paid		$ 144
First Quarter 2019 [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date		Dec. 12, 2018
Record Date		Feb. 15, 2019
Payment Date		Mar. 01, 2019
Dividends paid per share		$ 32.1563
Total dividends paid		$ 26
First Quarter 2019 [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date		Dec. 12, 2018
Record Date		Feb. 15, 2019
Payment Date		Mar. 01, 2019
Dividends paid per share		$ 17.5000
Total dividends paid		$ 17
First Quarter 2018 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date			Dec. 13, 2017
Record Date			Feb. 15, 2018
Payment Date			Mar. 08, 2018
Dividends paid per share			$ 0.2775
Total dividends paid			$ 120

[1] Amounts are included in the computation of net periodic cost and are reflected in Other income (expense), net in each of the Registrants’ respective Statements of Consolidated Income.

[2] Gains and losses are reclassified from Accumulated other comprehensive income into income when the hedged transactions affect earnings. The reclassification amounts are included in Interest and other finance charges in each of the Registrants’ respective Statements of Consolidated Income. O