STATEMENTS OF CONSOLIDATED SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series A Preferred Stock [Member]	Preferred Stock [Member] Series B Preferred Stock [Member]	Preferred Stock [Member] Series C Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Common Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series A Preferred Stock [Member]	Retained Earnings [Member] Series B Preferred Stock [Member]	Retained Earnings [Member] Series C Preferred Stock [Member]	AOCI Attributable to Parent [Member]	Houston Electric [Member]	Houston Electric [Member] Common Stock [Member]	Houston Electric [Member] Additional Paid-in Capital [Member]	Houston Electric [Member] Retained Earnings [Member]	Houston Electric [Member] AOCI Attributable to Parent [Member]	CERC Corp [Member]	CERC Corp [Member] Common Stock [Member]	CERC Corp [Member] Additional Paid-in Capital [Member]	CERC Corp [Member] Additional Paid-in Capital [Member] Discontinued Operations [Member]	CERC Corp [Member] Retained Earnings [Member]	CERC Corp [Member] AOCI Attributable to Parent [Member]
Balance, beginning of year at Dec. 31, 2017					0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances of stock						1,000,000	1,000,000	0	70,000,000
Balance, end of year at Dec. 31, 2018					2,000,000
Balance, beginning of year at Dec. 31, 2017									431,000,000									1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									0
Balance, end of year at Dec. 31, 2018									501,000,000									1,000					1,000
Balance, beginning of year at Dec. 31, 2017					$ 0				$ 4	$ 4,209		$ 543				$ (68)		$ 0	$ 1,696	$ 673	$ 0		$ 0	$ 2,528		$ 574	$ 6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									0	19
Issuances of stock						$ 790	$ 950	$ 0	1		$ 1,844
Number of depositary shares eligible for conversion (in shares)				0
Conversion of Stock, Amount Converted				$ 0
Conversion of Stock, Amount Issued								$ 0
Contribution From Parent																			200					960
Other																								0	$ 0
Capital distribution to parent associated with Internal Spin																								(1,473)
Net Income (Loss)	$ 368											368					$ 336			336		$ 208				208
Common Stock dividends declared (see Note 13)												(523)
Preferred stock dividends declared		$ (26)	$ (28)										$ (26)	$ (28)	$ 0
Adoption of ASU 2018-02 | Accounting Standards Update 2016-13 [Member]												0														0
Adoption of ASU 2018-02 | Accounting Standards Update 2018-02												15				(15)										1	(1)
Dividend to parent																				(209)						(360)
Other comprehensive income (loss)																(25)					(14)						0
Balance, end of year at Dec. 31, 2018	8,058				$ 1,740				$ 5	6,072		349				(108)	2,682	$ 0	1,896	800	(14)	2,443	$ 0	2,015		423	5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Beneficial Conversion Feature	0											0					0					0
Beneficial Conversion Feature	$ 0									0							0					0
Preferred Stock, $0.01 par value		$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, $0.01 par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Issuances of stock						0	0	0	0
Balance, end of year at Dec. 31, 2019		800,000	977,400		2,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									1,000,000
Balance, end of year at Dec. 31, 2019	502,242,061								502,000,000									1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									$ 0	8
Issuances of stock						$ 0	$ 0	$ 0	0		0
Number of depositary shares eligible for conversion (in shares)				0
Conversion of Stock, Amount Converted				$ 0
Conversion of Stock, Amount Issued							$ 0	$ 0
Contribution From Parent																			590					129
Other																								0	0
Capital distribution to parent associated with Internal Spin																								(28)
Net Income (Loss)	$ 791											791					356			356		212				212
Common Stock dividends declared (see Note 13)												(433)
Preferred stock dividends declared		$ (24)	$ (51)										(24)	(51)	0
Adoption of ASU 2018-02 | Accounting Standards Update 2016-13 [Member]												0														0
Adoption of ASU 2018-02 | Accounting Standards Update 2018-02												0				0										0	0
Dividend to parent																				(376)						(120)
Other comprehensive income (loss)																10					(1)						5
Balance, end of year at Dec. 31, 2019	8,359				$ 1,740				$ 5	6,080		632				(98)	3,251	$ 0	2,486	780	(15)	2,641	$ 0	2,116		515	10
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Beneficial Conversion Feature	0											0					0					0
Beneficial Conversion Feature	$ 0									0							0					0
Preferred Stock, $0.01 par value		$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, $0.01 par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Issuances of stock						0	0	1,000,000	48,000,000
Balance, end of year at Dec. 31, 2020		800,000	977,400	625,000	3,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									1,000,000
Balance, end of year at Dec. 31, 2020	551,355,861								551,000,000									1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans									$ 0	30
Issuances of stock						$ 0	$ 0	$ 723	1		$ 672
Number of depositary shares eligible for conversion (in shares)				0
Conversion of Stock, Amount Converted				$ (100)
Conversion of Stock, Amount Issued							$ 100	$ 100
Contribution From Parent																			62					217
Other																								(1)	$ (286)
Capital distribution to parent associated with Internal Spin																								0
Net Income (Loss)	$ (773)											(773)					334			334		81				81
Common Stock dividends declared (see Note 13)												(480)
Preferred stock dividends declared		$ (73)	$ (85)	$ (27)									$ (73)	$ (85)	$ (27)
Adoption of ASU 2018-02 | Accounting Standards Update 2016-13 [Member]												7														(5)
Adoption of ASU 2018-02 | Accounting Standards Update 2018-02												0				0										0	0
Dividend to parent																				(551)						(80)
Other comprehensive income (loss)																8					15						0
Balance, end of year at Dec. 31, 2020	8,348				$ 2,363				$ 6	6,914		(845)				$ (90)	3,111	$ 0	$ 2,548	$ 563	$ 0	2,567	$ 0	$ 2,046		$ 511	$ 10
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Beneficial Conversion Feature	(32)											$ (32)					0					0
Beneficial Conversion Feature	$ 32									$ 32							$ 0					$ 0
Preferred Stock, $0.01 par value		$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, $0.01 par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000