Equity (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended						9 Months Ended
		May 06, 2020	Apr. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 01, 2020
Class of Stock [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance												58,051,121
Dividends declared per share				$ 0.1500			$ 0.2875			$ 0.5900	$ 0.8625
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement				$ 36			$ 29			$ 102	$ 88
Amortization of Beneficial Conversion Feature				16			0			25	0
Total income allocated to preferred shareholders				52			29			127	88
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance				(84)		$ (98)	(105)		$ (108)	(98)	(108)
Other comprehensive income (loss) from unconsolidated affiliates				1			(2)			(2)	(2)
Prior service cost (2)	[1]									1	1
Actuarial losses (2)	[1]			2			2			5	6
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax										0	1
Reclassification of net deferred loss from cash flow hedges (3)	[2]									19	0
Tax expense				(1)			0			(7)	(2)
Net current period other comprehensive income (loss)				2			(2)			16	1
Ending Balance				$ (82)	$ (84)		$ (107)	$ (105)		(82)	(107)
Proceeds from Issuance of Common Stock										$ 672	$ 0
Common Stock [Member]
Class of Stock [Line Items]
Dividends paid per share										$ 0.5900	$ 0.8625
Total dividends paid										$ 309	$ 433
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Stock Issued During Period, Shares, New Issues		41,977,612		0			0			42,000,000	0
Shares Issued, Price Per Share		$ 16.08
Proceeds from Issuance of Common Stock		$ 673
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared				$ 30.6250			$ 30.6250			$ 61.2500	$ 62.7813
Dividends paid per share										$ 61.2500	$ 62.7813
Total dividends paid										$ 49	$ 50
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement				$ 12			$ 12			$ 37	$ 37
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared				$ 17.5000			$ 17.5000			$ 52.5000	$ 52.5000
Dividends paid per share										$ 52.5000	$ 52.5000
Total dividends paid										$ 51	$ 51
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement				$ 17			$ 17			$ 51	51
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Series C preferred stock		725,000
Convertible Preferred Stock, Shares Issued upon Conversion		47,354,670
Preferred Stock, Liquidation Preference Per Share		$ 1,000
Preferred stock dividends declared				$ 0.1500						$ 0.3000
Dividends paid per share										$ 0.3000
Total dividends paid										$ 14
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement				$ 7			0			14	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Proceeds from Issuance of Convertible Preferred Stock		$ 724
Preferred Stock, Convertible, Conversion Price		$ 15.31
Preferred Stock, Convertible, Conversion Limit		4.90%
Preferred Stock, Convertible, Percent Outstanding Shares To Amend		66 2/3%
Houston Electric [Member]
Preferred Stock Dividends and Other Adjustments [Abstract]
Amortization of Beneficial Conversion Feature										0	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance				0		(15)	(15)		(14)	(15)	(14)
Other comprehensive income (loss) from unconsolidated affiliates				0			0			0	0
Prior service cost (2)	[1]									0	0
Actuarial losses (2)	[1]			0			0			0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax										0	0
Reclassification of net deferred loss from cash flow hedges (3)	[2]									19	0
Tax expense				0			0			(4)	0
Net current period other comprehensive income (loss)				0			0			15	(1)
Ending Balance				0	0		(15)	(15)		0	(15)
CERC Corp [Member]
Preferred Stock Dividends and Other Adjustments [Abstract]
Amortization of Beneficial Conversion Feature										0	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance				10		$ 10	5		$ 5	10	5
Other comprehensive income (loss) from unconsolidated affiliates				0			0			0	0
Prior service cost (2)	[1]									0	0
Actuarial losses (2)	[1]			0			0			0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax										0	0
Reclassification of net deferred loss from cash flow hedges (3)	[2]									0	0
Tax expense				0			0			0	0
Net current period other comprehensive income (loss)				0			0			0	0
Ending Balance				10	$ 10		5	$ 5		10	5
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Deferred gain (loss) from interest rate derivatives (1)	[3]			0			(2)			0	(3)
Interest Rate Contract [Member] | Houston Electric [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Deferred gain (loss) from interest rate derivatives (1)	[3]			0			0			0	(1)
Interest Rate Contract [Member] | CERC Corp [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Deferred gain (loss) from interest rate derivatives (1)	[3]			$ 0			0			$ 0	$ 0
First Quarter 2020 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date						Feb. 03, 2020
Record Date						Feb. 20, 2020
Payment Date						Mar. 12, 2020
Dividends paid per share						$ 0.2900
Total dividends paid						$ 145
First Quarter 2020 [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date						Feb. 03, 2020
Record Date						Feb. 14, 2020
Payment Date						Mar. 02, 2020
Dividends paid per share						$ 30.6250
Total dividends paid						$ 25
First Quarter 2020 [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date						Feb. 03, 2020
Record Date						Feb. 14, 2020
Payment Date						Mar. 02, 2020
Dividends paid per share						$ 17.5000
Total dividends paid						$ 17
Second Quarter 2020 [Member] | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date					Apr. 24, 2020
Record Date					May 21, 2020
Payment Date					Jun. 11, 2020
Dividends paid per share					$ 0.1500
Total dividends paid					$ 82
Second Quarter 2020 [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date					Apr. 24, 2020
Record Date					May 15, 2020
Payment Date					Jun. 01, 2020
Dividends paid per share					$ 17.5000
Total dividends paid					$ 17
Second Quarter 2020 [Member] | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date	[4]				Apr. 24, 2020
Record Date					May 21, 2020
Payment Date					Jun. 11, 2020
Dividends paid per share					$ 0.1500
Total dividends paid					$ 7
Third Quarter 2020 | Common Stock [Member]
Class of Stock [Line Items]
Declaration Date				Jul. 29, 2020
Record Date				Aug. 20, 2020
Payment Date				Sep. 10, 2020
Dividends paid per share				$ 0.1500
Total dividends paid				$ 82
Third Quarter 2020 | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date				Jul. 29, 2020
Record Date				Aug. 14, 2020
Payment Date				Sep. 01, 2020
Dividends paid per share				$ 30.6250
Total dividends paid				$ 24
Third Quarter 2020 | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date				Jul. 29, 2020
Record Date				Aug. 14, 2020
Payment Date				Sep. 01, 2020
Dividends paid per share				$ 17.5000
Total dividends paid				$ 17
Third Quarter 2020 | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date				Jul. 29, 2020
Record Date				Aug. 20, 2020
Payment Date				Sep. 10, 2020
Dividends paid per share				$ 0.1500
Total dividends paid				$ 7
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							$ 145	$ 144
Second Quarter 2019 [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Declaration Date								Apr. 25, 2019
Record Date								May 15, 2019
Payment Date								Jun. 03, 2019
Dividends paid per share								$ 17.5000
Total dividends paid								$ 17
Third Quarter 2019 | 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
Third Quarter 2019 | 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
Third Quarter 2019 | Series B 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							$ 17.5000
Total dividends paid							$ 17
Previous Dividend or Distribution [Member] | Common Stock [Member]
Class of Stock [Line Items]
Dividends declared per share			$ 0.2900
Revised Dividend or Distribution [Member] | Common Stock [Member]
Class of Stock [Line Items]
Dividends declared per share			$ 0.1500

[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] The cost of debt approved by the PUCT as part of Houston Electric’s Stipulation and Settlement Agreement included unrealized gains and losses on interest rate hedges. Accordingly, deferred gains and losses on interest rate hedges were reclassified to regulatory assets or liabilities, as appropriate.

[3] 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.

[4] Declaration date for dividends on Common Stock. The Series C Preferred Stock is entitled to participate in any dividend or distribution (excluding those payable in Common Stock) with the Common Stock on a pari passu, pro rata, as-converted basis. The per share amount reflects the dividend per share of Common Stock as if the Series C Preferred Stock were converted into Common Stock.