Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax expense (benefit):
Total deferred expense (benefit)	$ (429)	$ 69	$ 48
Total income tax expense (benefit)	(274)	92	155
Income tax reconciliation [Abstract]
Income (loss) before income taxes	(865)	774	551
Income (loss) before income taxes	37	155	(37)
Increase (decrease) in tax expense resulting from:
State valuation allowance, net of federal income tax		4	11
State law change, net of federal income tax	39		32
Excess deferred income tax amortization	(76)	(55)	(24)
Total income tax expense (benefit)	(274)	92	155
Deferred tax assets:
Benefits and compensation	141	152
Regulatory liabilities	435	447
Loss and credit carryforwards	103	111
Asset retirement obligations	152	89
Deferred Tax Assets, Derivative Instruments	47	34
Other	52	40
Valuation allowance	(26)	(25)
Total deferred tax assets	904	848
Deferred tax liabilities:
Property, plant, and equipment	2,790	2,656
Investment in unconsolidated affiliates	624	1,010
Regulatory assets	325	344
Investment in marketable securities and indexed debt	649	586
Other	119	180
Total deferred tax liabilities	4,507	4,776
Net deferred tax liabilities	3,603	3,928
Reconciliation of Unrecognized Tax Benefits, excluding interest and penalties:
Balance, beginning of year	8	0
Unrecognized tax benefits assumed through the Merger	0	9
Increases related to tax positions of prior years	3	0
Decreases related to tax positions of prior years	(4)	(1)
Balance, end of year	7	8	0
State and Local Jurisdiction
Increase (decrease) in tax expense resulting from:
Federal income tax rate reduction		(21)
Deferred tax liabilities:
Operating loss carryforwards	979
Deferred tax assets tax credit carryforwards	22
Houston Electric [Member]
Current income tax expense (benefit):
Federal	76	84	109
State	19	20	18
Total current expense (benefit)	95	104	127
Deferred income tax expense (benefit):
Federal	(42)	(24)	(38)
Total deferred expense (benefit)	(42)	(24)	(38)
Total income tax expense (benefit)	53	80	89
Income tax reconciliation [Abstract]
Income (loss) before income taxes	$ 387	$ 436	$ 425
Federal statutory income tax rate	21.00%	21.00%	21.00%
Expected federal income tax expense (benefit)	$ 81	$ 92	$ 89
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	15	16	14
Excess deferred income tax amortization	(42)	(21)	(9)
Other, net	(1)	(7)	(5)
Total	(28)	(12)	0
Total income tax expense (benefit)	$ 53	$ 80	$ 89
Effective tax rate (in hundredths)	14.00%	18.00%	21.00%
Deferred tax assets:
Benefits and compensation	$ 17	$ 14
Regulatory liabilities	201	195
Asset retirement obligations	9	9
Other	9	7
Total deferred tax assets	236	225
Deferred tax liabilities:
Property, plant, and equipment	1,159	1,129
Regulatory assets	118	126
Total deferred tax liabilities	1,277	1,255
Net deferred tax liabilities	1,041	1,030
CERC Corp [Member]
Deferred income tax expense (benefit):
Total deferred expense (benefit)	91	7	$ 64
Total income tax expense (benefit)	97	(3)	31
Income tax reconciliation [Abstract]
Income (loss) before income taxes	244	186	129
Increase (decrease) in tax expense resulting from:
State valuation allowance, net of federal income tax		4
Excess deferred income tax amortization	(16)	(18)
Total income tax expense (benefit)	97	(3)	31
Deferred tax assets:
Valuation allowance	(15)
CERC Corp [Member] | State and Local Jurisdiction
Increase (decrease) in tax expense resulting from:
Federal income tax rate reduction		(4)
Deferred tax liabilities:
Operating loss carryforwards	592
Deferred tax assets tax credit carryforwards	17
CERC Corp [Member] | Domestic Tax Authority
Deferred tax liabilities:
Deferred tax assets tax credit carryforwards	425
Continuing Operations [Member]
Current income tax expense (benefit):
Federal	(1)	30	77
State	32	15	6
Total current expense (benefit)	31	45	83
Deferred income tax expense (benefit):
Federal	(257)	55	(6)
State	(48)	(8)	78
Total deferred expense (benefit)	(305)	47	72
Total income tax expense (benefit)	(274)	92	155
Income tax reconciliation [Abstract]
Income (loss) before income taxes	$ (865)	$ 774	$ 551
Federal statutory income tax rate	21.00%	21.00%	21.00%
Expected federal income tax expense (benefit)	$ (182)	$ 163	$ 116
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	(15)	30	23
State valuation allowance, net of federal income tax	1	(4)	11
State law change, net of federal income tax	0	(21)	32
Goodwill impairment	39	0	0
Net operating loss carryback	(37)	0	0
Excess deferred income tax amortization	(76)	(55)	(24)
Other, net	(4)	(21)	(3)
Total	(92)	(71)	39
Total income tax expense (benefit)	$ (274)	$ 92	$ 155
Effective tax rate (in hundredths)	32.00%	12.00%	28.00%
Continuing Operations [Member] | CERC Corp [Member]
Current income tax expense (benefit):
State	$ 4	$ 5	$ (3)
Total current expense (benefit)	4	5	(3)
Deferred income tax expense (benefit):
Total deferred expense (benefit)	93	(8)	34
Total income tax expense (benefit)	97	(3)	31
Income tax reconciliation [Abstract]
Income (loss) before income taxes	$ 244	$ 186	$ 129
Federal statutory income tax rate	21.00%	21.00%	21.00%
Expected federal income tax expense (benefit)	$ 51	$ 39	$ 27
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	55	(15)	5
State law change, net of federal income tax	0	(4)	0
Excess deferred income tax amortization	(16)	(18)	(15)
Other, net	6	(1)	3
Total	46	(42)	4
Total income tax expense (benefit)	$ 97	$ (3)	$ 31
Effective tax rate (in hundredths)	40.00%	(2.00%)	24.00%
Deferred tax assets:
Benefits and compensation	$ 28	$ 24
Regulatory liabilities	147	144
Loss and credit carryforwards	143	183
Asset retirement obligations	140	80
Other	26	23
Valuation allowance	(15)	(15)
Total deferred tax assets	469	439
Deferred tax liabilities:
Property, plant, and equipment	916	821
Regulatory assets	53	45
Other	84	43
Total deferred tax liabilities	1,053	909
Net deferred tax liabilities	584	470
Continuing Operations [Member] | CERC Corp [Member] | State and Local Jurisdiction
Deferred income tax expense (benefit):
Federal	67
State		(34)	$ 25
Continuing Operations [Member] | CERC Corp [Member] | Domestic Tax Authority
Deferred income tax expense (benefit):
Federal	26	26	9
Discontinued Operations [Member]
Current income tax expense (benefit):
Federal	117	18	12
State	28	6	3
Total current expense (benefit)	145	24	15
Deferred income tax expense (benefit):
Federal	(102)	19	(19)
State	(22)	3	(5)
Total deferred expense (benefit)	(124)	22	(24)
Total income tax expense (benefit)	21	46	(9)
Income tax reconciliation [Abstract]
Income (loss) before income taxes	$ (161)	$ 155	$ (37)
Federal statutory income tax rate	21.00%	21.00%	21.00%
Expected federal income tax expense (benefit)	$ (34)	$ 32	$ (8)
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	(5)	6	(1)
Goodwill impairment	25	8	0
Tax impact of sale of Energy Services and Infrastructure Services Disposal Groups	30	0	0
Other, net	5	0	0
Total	55	14	(1)
Total income tax expense (benefit)	$ 21	$ 46	$ (9)
Effective tax rate (in hundredths)	(13.00%)	30.00%	24.00%
Discontinued Operations [Member] | CERC Corp [Member]
Current income tax expense (benefit):
State	$ 0	$ 2	$ 7
Total current expense (benefit)	0	2	7
Deferred income tax expense (benefit):
Federal	0	13	30
State	(2)	2	0
Total deferred expense (benefit)	(2)	15	30
Total income tax expense (benefit)	(2)	17	37
Income tax reconciliation [Abstract]
Income (loss) before income taxes	$ (68)	$ 40	$ 147
Federal statutory income tax rate	21.00%	21.00%	21.00%
Expected federal income tax expense (benefit)	$ (14)	$ 8	$ 31
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	(2)	3	7
Goodwill impairment	10	8	0
Other, net	4	(2)	(1)
Total	12	9	6
Total income tax expense (benefit)	$ (2)	$ 17	$ 37
Effective tax rate (in hundredths)	3.00%	43.00%	25.00%
State Valuation Allowance, net of Federal Income Taxes [Member] | Continuing Operations [Member] | CERC Corp [Member]
Increase (decrease) in tax expense resulting from:
State valuation allowance, net of federal income tax	$ 1	$ (4)	$ 11
Vectren [Member]
Deferred tax liabilities:
Operating loss carryforwards	177
Reconciliation of Unrecognized Tax Benefits, excluding interest and penalties:
Unrecognized tax benefits assumed through the Merger	9	$ 9
Vectren [Member] | Charitable Contribution [Member]
Deferred tax liabilities:
Deferred tax assets tax credit carryforwards	$ 60