Condensed Statements of Consolidated Changes in Equity - USD ($) $ in Millions	Total	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]	Common Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series A Preferred Stock [Member]	Retained Earnings [Member] Series B Preferred Stock [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] Retained Earnings [Member]	CERC Corp [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]
Balance, beginning of period at Dec. 31, 2017					0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		1,000,000
Balance, end of period at Sep. 30, 2018					1,000,000
Balance, beginning of period 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 period at Sep. 30, 2018						431,000,000							1,000					1,000
Balance, beginning of period at Dec. 31, 2017					$ 0	$ 4	$ 4,209	$ 543			$ (68)		$ 0	$ 2,528	$ 574	$ 6		$ 0	$ 1,696	$ 673	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Value, New Issues		$ 790
Issuances related to benefit and investment plans						0	12
Other Significant Noncash Transaction, Value of Consideration Given												$ (1,460)		(1,460)
Contribution From Parent														600					0
Other																			0
Net income (Loss)	$ 248							248				175			175		$ 296			296
Dividends, Common Stock, Cash				$ (360)				(240)
Dividend to parent															(286)					(123)
Other comprehensive income (loss)											10										7
Balance, end of period at Sep. 30, 2018	5,508				$ 790	$ 4	4,221	551			(58)	2,137	$ 0	1,668	463	6	2,549	$ 0	1,696	846	7
Balance, beginning of period at Jun. 30, 2018					0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		1,000,000
Balance, end of period at Sep. 30, 2018					1,000,000
Balance, beginning of period at Jun. 30, 2018						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 period at Sep. 30, 2018						431,000,000							1,000					1,000
Balance, beginning of period at Jun. 30, 2018					$ 0	$ 4	4,215	513			(62)		$ 0	2,528	529	6		$ 0	1,697	763	4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Value, New Issues		$ 790
Issuances related to benefit and investment plans						0	6
Other Significant Noncash Transaction, Value of Consideration Given												(1,460)		(1,460)
Contribution From Parent														600					0
Other																			(1)
Net income (Loss)	158							158				9			9		143			143
Dividends, Common Stock, Cash								(120)
Dividend to parent															(75)					(60)
Other comprehensive income (loss)											4										3
Balance, end of period at Sep. 30, 2018	$ 5,508				$ 790	$ 4	4,221	551			(58)	2,137	$ 0	1,668	463	6	2,549	$ 0	1,696	846	7
Cumulative preferred stock authorized (in shares)	20,000,000
Balance, beginning of period at Dec. 31, 2018		800,000	977,500		2,000,000
Balance, end of period at Sep. 30, 2019		800,000	977,500		2,000,000
Balance, beginning of period at Dec. 31, 2018	501,197,784					501,000,000							1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans						1,000,000
Balance, end of period at Sep. 30, 2019	502,235,354					502,000,000							1,000					1,000
Balance, beginning of period at Dec. 31, 2018	$ 8,058				$ 1,740	$ 5	6,072	349			(108)	2,443	$ 0	2,015	423	5	2,682	$ 0	1,896	800	(14)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans						0	0
Other Significant Noncash Transaction, Value of Consideration Given												0
Contribution From Parent																			590
Other																			0
Net income (Loss)	634							634				159			159		312			312
Dividends, Common Stock, Cash				$ (433)				(289)
Dividends, Preferred Stock, Cash		$ (50)	$ (51)						$ (24)	$ (34)
Dividend to parent															(119)					(100)
Other comprehensive income (loss)											1										(1)
Balance, end of period at Sep. 30, 2019	$ 8,346				$ 1,740	$ 5	6,072	636			(107)	2,483	$ 0	2,015	463	5	3,483	$ 0	2,486	1,012	(15)
Balance, beginning of period at Jun. 30, 2019					2,000,000
Balance, end of period at Sep. 30, 2019		800,000	977,500		2,000,000
Balance, beginning of period at Jun. 30, 2019						502,000,000							1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans						0
Balance, end of period at Sep. 30, 2019	502,235,354					502,000,000							1,000					1,000
Balance, beginning of period at Jun. 30, 2019					$ 1,740	$ 5	6,065	552			(105)		$ 0	2,015	486	5		$ 0	2,486	887	(15)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans						0	7
Other Significant Noncash Transaction, Value of Consideration Given												0
Contribution From Parent																			0
Other																			0
Net income (Loss)	$ 270							270				(7)			(7)		185			185
Dividends, Common Stock, Cash								(145)
Dividends, Preferred Stock, Cash									$ (24)	$ (17)
Dividend to parent															(16)					(60)
Other comprehensive income (loss)											(2)										0
Balance, end of period at Sep. 30, 2019	$ 8,346				$ 1,740	$ 5	$ 6,072	$ 636			$ (107)	$ 2,483	$ 0	$ 2,015	$ 463	$ 5	$ 3,483	$ 0	$ 2,486	$ 1,012	$ (15)
Cumulative preferred stock authorized (in shares)	20,000,000