Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 32,514	$ 30,324
Accumulated Depreciation, and Amortization	10,152	9,700
Property, Plant and Equipment, Net	22,362	20,624
Depreciation and Amortization [Abstract]
Depreciation	961	879	$ 623
Amortization of securitized regulatory assets	155	271	531
Other amortization	73	75	76
Total	1,189	1,225	1,230
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	539	258
Asset Retirement Obligation Addition from Merger with Vectren	0	116
Accretion expense (1)	16	16
Revisions in estimates (2)	232	149
Ending balance	787	539	258
Houston Electric [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	13,593	12,829
Accumulated Depreciation, and Amortization	3,930	3,797
Property, Plant and Equipment, Net	9,663	9,032
Depreciation and Amortization [Abstract]
Depreciation	368	339	342
Amortization of securitized regulatory assets	155	271	531
Other amortization	37	38	44
Total	560	648	917
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	42	34
Asset Retirement Obligation Addition from Merger with Vectren	0	0
Accretion expense (1)	1	1
Revisions in estimates (2)	0	7
Ending balance	43	42	34
CERC Corp [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	8,972	8,079
Accumulated Depreciation, and Amortization	2,414	2,270
Property, Plant and Equipment, Net	6,558	5,809
Depreciation and Amortization [Abstract]
Depreciation	289	277	261
Amortization of securitized regulatory assets	0	0	0
Other amortization	15	16	19
Total	304	293	280
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	325	221
Asset Retirement Obligation Addition from Merger with Vectren	0	0
Accretion expense (1)	11	10
Revisions in estimates (2)	235	94
Ending balance	571	325	$ 221
Electric Transmission and Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	15,225	14,360
Accumulated Depreciation, and Amortization	4,785	4,634
Property, Plant and Equipment, Net	10,440	9,726
Electric Generation Equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	1,922	1,780
Accumulated Depreciation, and Amortization	754	698
Property, Plant and Equipment, Net	$ 1,168	1,082
Electric Generation Equipment [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	27 years
Electric Transmission [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	36 years
Electric Transmission [Member] | Houston Electric [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 3,686	3,358
Accumulated Depreciation, and Amortization	700	674
Property, Plant and Equipment, Net	$ 2,986	2,684
Electric Transmission [Member] | Houston Electric [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	46 years
Electric Distribution [Member] | Houston Electric [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 8,225	7,876
Accumulated Depreciation, and Amortization	2,696	2,586
Property, Plant and Equipment, Net	$ 5,529	5,290
Electric Distribution [Member] | Houston Electric [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	34 years
Natural Gas Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 14,022	12,787
Accumulated Depreciation, and Amortization	4,019	3,766
Property, Plant and Equipment, Net	$ 10,003	9,021
Natural Gas Distribution [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	29 years
Natural Gas Distribution [Member] | CERC Corp [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 8,928	8,024
Accumulated Depreciation, and Amortization	2,392	2,243
Property, Plant and Equipment, Net	$ 6,536	5,781
Natural Gas Distribution [Member] | CERC Corp [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	29 years
Other property [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 1,345	1,397
Accumulated Depreciation, and Amortization	594	602
Property, Plant and Equipment, Net	$ 751	795
Other property [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	15 years
Other property [Member] | Houston Electric [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 1,682	1,595
Accumulated Depreciation, and Amortization	534	537
Property, Plant and Equipment, Net	$ 1,148	1,058
Other property [Member] | Houston Electric [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	22 years
Other property [Member] | CERC Corp [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 44	55
Accumulated Depreciation, and Amortization	22	27
Property, Plant and Equipment, Net	$ 22	$ 28
Other property [Member] | CERC Corp [Member] | Weighted Average [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Useful Lives	19 years
SIGECO [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
SIGECO's share of cost of Warrick Unit 4	$ 195
SIGECO's share of accumulated depreciation of Warrick Unit 4	$ 146