Equity (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Dividends declared per share		$ 0.2875			$ 0.2775			$ 0.5750	$ 0.5550
Preferred stock dividend requirement		$ 29			$ 5			$ 88	$ 5
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(105)		$ (108)	(62)		$ (68)	(108)	(68)
Other comprehensive loss from unconsolidated affiliates, net of tax		(2)			0			(2)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	[1]							1	1
Actuarial losses	[1]	2			2			6	5
Reclassification of deferred loss from cash flow hedges realized in net income								1	0
Tax expense		0			(2)			(2)	(4)
Net current period other comprehensive income (loss)		(2)			4			1	10
Ending Balance		$ (107)	$ (105)		$ (58)	$ (62)		$ (107)	$ (58)
Common Stock [Member]
Class of Stock [Line Items]
Dividends declared per share		$ 0.2875			$ 0.2775			$ 0.2875	$ 0.2775
Dividends paid per share								$ 0.8625	$ 0.8325
Total dividends paid								$ 433	$ 360
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 30.6250			$ 0.0000			$ 30.6250	$ 0.0000
Dividends paid per share								$ 62.7813
Total dividends paid								$ 50
Preferred stock dividend requirement		$ 12			$ 5			$ 37	$ 5
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 17.5000			$ 0.0000			$ 35.0000	$ 0.0000
Dividends paid per share								$ 52.5000
Total dividends paid								$ 51
Preferred stock dividend requirement		$ 17			$ 0			51	$ 0
Houston Electric [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(15)		(14)	4		0	(14)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	[1]							0	0
Actuarial losses	[1]	0			0				0
Reclassification of deferred loss from cash flow hedges realized in net income								0	0
Tax expense		0			0			0	(1)
Net current period other comprehensive income (loss)		0			3			(1)	7
Ending Balance		(15)	(15)		7	4		(15)	7
CERC Corp [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		5		$ 5	6		$ 6	5	6
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	[1]							0	0
Actuarial losses	[1]	0			0			0	0
Reclassification of deferred loss from cash flow hedges realized in net income								0	0
Tax expense		0			0			0	0
Net current period other comprehensive income (loss)		0			0			0	0
Ending Balance		5	$ 5		6	$ 6		5	6
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	(2)			4			(3)	8
Interest Rate Contract [Member] | Houston Electric [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	0			3			(1)	8
Interest Rate Contract [Member] | CERC Corp [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	[2]	$ 0			$ 0			$ 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
Second Quarter 2019 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date			Apr. 25, 2019
Record Date			May 16, 2019
Payment Date			Jun. 13, 2019
Dividends paid per share			$ 0.2875
Total dividends paid			$ 144
Second Quarter 2019 [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date		Jul. 31, 2019	Apr. 25, 2019
Record Date		Aug. 15, 2019	May 15, 2019
Payment Date		Sep. 03, 2019	Jun. 03, 2019
Dividends paid per share		$ 17.5000	$ 17.5000
Total dividends paid		$ 17	$ 17
Third Quarter 2019 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date		Jul. 31, 2019
Record Date		Aug. 15, 2019
Payment Date		Sep. 12, 2019
Dividends paid per share		$ 0.2875
Total dividends paid		$ 145
Third Quarter 2019 [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date		Jul. 31, 2019
Record Date		Aug. 15, 2019
Payment Date		Sep. 03, 2019
Dividends paid per share		$ 30.6250
Total dividends paid		$ 24
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
Second Quarter 2018 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date						Apr. 26, 2018
Record Date						May 17, 2018
Payment Date						Jun. 14, 2018
Dividends paid per share						$ 0.2775
Total dividends paid						$ 120
Third Quarter 2018 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date					Jul. 26, 2018
Record Date					Aug. 16, 2018
Payment Date					Sep. 13, 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. Over the next twelve months estimated amortization from Accumulated Comprehensive Income into income is expected to be immaterial.