Reportable Business Segments (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Sep. 04, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues		$ 2,212		$ 2,098	$ 7,553		$ 6,976
Operating Income (Loss)		226		297	664		828
Equity in earnings from investment in Enable		81		68	208		199
Assets		22,228			22,228				$ 22,736
Total regulatory assets		1,994			1,994				2,477
Electric Transmission and Distribution [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	897		843	2,502		2,234
Operating Income (Loss)		227		254	523		511
Electric Transmission and Distribution [Member] | Affiliates of NRG Energy, Inc. [Member]
Segment Reporting Information [Line Items]
Revenues		213		221	543		540
Electric Transmission and Distribution [Member] | Affiliates of Vistra Energy Corp. [Member]
Segment Reporting Information [Line Items]
Revenues		79		72	192		172
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues		402		390	2,032		1,767
Operating Income (Loss)		3		25	166		235
Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues		910		861	3,008		2,964
Operating Income (Loss)		(9)		7	(20)		58
Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	0		0	0		0
Operating Income (Loss)	[2]	0		0	0		0
Equity in earnings from investment in Enable		81		68	208		199
Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues		3		4	11		11
Operating Income (Loss)		5		11	(5)		24
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(18)		(18)	(83)		(58)
Assets		(681)			(681)				(654)
Intersegment Eliminations [Member] | Electric Transmission and Distribution [Member]
Segment Reporting Information [Line Items]
Revenues		0		0	0		0
Intersegment Eliminations [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues		(8)		(8)	(26)		(24)
Intersegment Eliminations [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues		(10)		(10)	(57)		(34)
Intersegment Eliminations [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	0		0	0		0
Intersegment Eliminations [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues		0		0	0		0
Operating Segments [Member] | Electric Transmission and Distribution [Member]
Segment Reporting Information [Line Items]
Assets		10,436			10,436				10,292
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Assets		6,557			6,557				6,608
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Assets		1,253			1,253				1,521
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Assets		2,457			2,457				2,472
Operating Segments [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Assets	[3]	2,206			2,206				2,497
Pension and Other Postretirement Plans Costs [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Total regulatory assets		566			566				600
CERC Corp [Member]
Segment Reporting Information [Line Items]
Revenues		1,312		1,251	5,040		4,731
Operating Income (Loss)		(7)		31	146		289
Assets		7,305			7,305				10,112
Assets of discontinued operations		0			0				2,472
Total regulatory assets		230			230				311
CERC Corp [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues		402		390	2,032		1,767
Operating Income (Loss)		3		25	166		235
CERC Corp [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues		910		861	3,008		2,964
Operating Income (Loss)		(9)		7	(20)		58
CERC Corp [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues		0		0	0		0
Operating Income (Loss)		(1)		(1)	0		(4)
CERC Corp [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(18)		(18)	(83)		(58)
Assets		(615)			(615)				(559)
CERC Corp [Member] | Intersegment Eliminations [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues		(8)		(8)	(26)		(24)
CERC Corp [Member] | Intersegment Eliminations [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues		(10)		(10)	(57)		(34)
CERC Corp [Member] | Intersegment Eliminations [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues		0		$ 0	0		$ 0
CERC Corp [Member] | Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Assets		6,557			6,557				6,608
CERC Corp [Member] | Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Assets		1,253			1,253				1,521
CERC Corp [Member] | Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Assets		0			0				0
CERC Corp [Member] | Operating Segments [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Assets		110			110				70
Enable Midstream Partners [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | CERC Corp [Member]
Segment Reporting Information [Line Items]
Assets of discontinued operations		$ 0	[4]		$ 0	[4]		$ 2,400	$ 2,472	[4]

[1] CenterPoint Energy’s and Houston Electric’s Electric Transmission & Distribution revenues from major customers are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (in millions)Affiliates of NRG $213 $221 $543 $540Affiliates of Vistra Energy Corp. 79 72 192 172

[2] CenterPoint Energy’s Midstream Investments’ equity earnings, net are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 (in millions)Enable $81 $68 $208 $199

[3] Includes pension and other postemployment-related regulatory assets of $566 million and $600 million, respectively, as of September 30, 2018 and December 31, 2017.

[4] On September 4, 2018, CERC completed the Internal Spin. For further information regarding the Internal Spin, see Note 9.