Reportable Segments Financial Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating revenues	$ 7,418	$ 7,564	$ 6,277
Equity in earnings (loss) of unconsolidated affiliates, net	(1,428)	230	307
Depreciation and Amortization	1,189	1,225	1,230
Interest Income	3	17	24
Interest Expense	(501)	(528)	(361)
Income Tax Expense (Benefit)	(274)	92	155
Net income (loss)	(773)	791	368
Total Assets	33,471	35,529	27,093
Expenditures for Long-Lived Assets	2,536	2,587	1,720
Regulatory Assets	2,127	2,129
Income (Loss) from Discontinued Operations	(182)	109	(28)
Continuing Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	7,418	7,564	6,277
Equity in earnings (loss) of unconsolidated affiliates, net	(1,428)	230	307
Depreciation and Amortization	1,189	1,225	1,230
Interest Income	4	22	28
Interest Expense	(529)	(567)	(420)
Income Tax Expense (Benefit)	(274)	92	155
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(591)	682	396
Total Assets	33,471	33,565	25,984
Expenditures for Long-Lived Assets	2,515	2,508	1,700
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	21	46	(9)
Total Assets	0	1,964	1,109
Expenditures for Long-Lived Assets	21	79	20
Income (Loss) from Discontinued Operations	(182)	109	(28)
Electric | Affiliates of NRG Energy, Inc. [Member]
Segment Reporting Information [Line Items]
Operating revenues	749	727	705
Electric | Affiliates of Vistra Energy Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenues	404	263	251
Operating Segments [Member] | Electric
Segment Reporting Information [Line Items]
Operating revenues	3,470	3,519	3,232
Equity in earnings (loss) of unconsolidated affiliates, net	0	0	0
Depreciation and Amortization	663	739	917
Interest Income	3	27	5
Interest Expense	(220)	(225)	(197)
Income Tax Expense (Benefit)	72	96	89
Net income (loss)	230	419	334
Total Assets	14,493	14,432	10,509
Expenditures for Long-Lived Assets	1,281	1,216	952
Operating Segments [Member] | Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,631	3,750	3,031
Equity in earnings (loss) of unconsolidated affiliates, net	0	0	0
Depreciation and Amortization	454	420	280
Interest Income	8	6	1
Interest Expense	(153)	(144)	(122)
Income Tax Expense (Benefit)	125	2	31
Net income (loss)	278	251	98
Total Assets	14,976	14,002	7,188
Expenditures for Long-Lived Assets	1,139	1,098	638
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0
Equity in earnings (loss) of unconsolidated affiliates, net	(1,428)	229	307
Depreciation and Amortization	0	0	0
Interest Income	1	8	0
Interest Expense	(54)	(53)	(10)
Income Tax Expense (Benefit)	(364)	53	73
Net income (loss)	(1,116)	131	224
Total Assets	913	2,473	2,482
Expenditures for Long-Lived Assets	0	0	0
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	317	295	14
Equity in earnings (loss) of unconsolidated affiliates, net	0	1	0
Depreciation and Amortization	72	66	33
Interest Income	103	126	66
Interest Expense	(213)	(290)	(135)
Income Tax Expense (Benefit)	(107)	(59)	(38)
Net income (loss)	17	(119)	(260)
Total Assets	3,089	2,658	5,805
Expenditures for Long-Lived Assets	95	194	110
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0
Equity in earnings (loss) of unconsolidated affiliates, net	0	0	0
Depreciation and Amortization	0	0	0
Interest Income	(111)	(145)	(44)
Interest Expense	111	145	44
Income Tax Expense (Benefit)	0	0	0
Net income (loss)	0	0	0
Houston Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,911	2,990	3,234
Depreciation and Amortization	560	648	917
Interest Income	2	22	1
Interest Expense	(171)	(164)	(138)
Income Tax Expense (Benefit)	53	80	89
Net income (loss)	334	356	336
Total Assets	11,316	11,262
Regulatory Assets	848	915
Houston Electric [Member] | Electric Transmission & Distribution [Member] | Affiliates of NRG Energy, Inc. [Member]
Segment Reporting Information [Line Items]
Operating revenues	749	727	705
Houston Electric [Member] | Electric Transmission & Distribution [Member] | Affiliates of Vistra Energy Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenues	404	263	251
CERC Corp [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,763	3,018	3,031
Equity in earnings (loss) of unconsolidated affiliates, net	0	0	184
Depreciation and Amortization	304	293	280
Interest Income	0	5	1
Interest Expense	(111)	(116)	(122)
Income Tax Expense (Benefit)	97	(3)	31
Net income (loss)	81	212	208
Total Assets	8,308	8,512
Regulatory Assets	253	203
Income (Loss) from Discontinued Operations	(66)	23	110
CERC Corp [Member] | Continuing Operations [Member]
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	97	(3)	31
CERC Corp [Member] | Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	(2)	17	37
Pension and Other Postretirement Plans Costs [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Regulatory Assets	540	$ 584	$ 665
Cash and Cash Equivalents [Member]
Segment Reporting Information [Line Items]
Short-term Investments	$ 3,900