Unconsolidated Affiliate (CenterPoint Energy and CERC) (Details) - USD ($) $ / shares in Units, $ 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
Enable Units [Abstract]
Preferred units – unconsolidated affiliate		$ 363			$ 363				$ 363
Percentage of sales that trigger right of first refusal					5.00%
Enable Distributions [Abstract]
Total distributions received from Enable		83		$ 83	$ 250		$ 250
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract]
Equity in earnings of unconsolidated affiliate, net		81		68	208		199
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s equity method investment in Enable		2,457			2,457				2,472
CERC Corp [Member]
Investment in unconsolidated affiliate - discontinued operations		0			0				2,472
Deferred income taxes, net - discontinued operations		0			0				927
Contribution from parent		600		0	600		38
Enable Distributions [Abstract]
Total distributions received from Enable	[1]	74		74	223		223
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Income tax expense		13		26	44		75
Income from discontinued operations (net of tax of $13, $26, $44 and $75, respectively)		$ 44		42	$ 140		124
OGE [Member]
Enable Units [Abstract]
Percentage of sales that trigger right of first refusal					5.00%
Enable Midstream Partners [Member]
Enable Partnership Interest [Abstract]
Ownership percentage of equity method investment	[2],[3]	54.00%			54.00%
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract]
Operating revenues		$ 928		705	$ 2,481		1,997
Cost of sales, excluding depreciation and amortization		516		349	1,335		936
Depreciation and amortization		100		90	292		267
Operating income		171		137	436		399
Net income attributable to Enable common units		129		104	320		301
CenterPoint Energy’s interest		70		56	173		163
Basis difference amortization (1)	[4]	11		12	35		36
Equity in earnings of unconsolidated affiliate, net		81		68	$ 208		199
Basis difference amortization period					31 years
Equity Method Investment, Summarized Financial Information, Assets and Liabilities [Abstract]
Current assets		481			$ 481				416
Non-current assets		11,454			11,454				11,177
Current liabilities		1,403			1,403				1,279
Non-current liabilities		2,964			2,964				2,660
Non-controlling interest		11			11				12
Preferred equity		362			362				362
Enable partners’ equity		7,195			7,195				7,280
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s ownership interest in Enable partners’ equity		3,883			3,883				3,935
CenterPoint Energy’s basis difference		(1,426)			(1,426)				(1,463)
CenterPoint Energy’s equity method investment in Enable		2,457			2,457				2,472
Enable Midstream Partners [Member] | Common Units [Member]
Enable Distributions [Abstract]
Distributions received from Enable equity method investment	[5]	74		74	223		223
Enable Midstream Partners [Member] | Series A Preferred Units [Member]
Enable Distributions [Abstract]
Distributions received from Enable cost method investment	[6]	$ 9		9	$ 27		27
Common Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Limited partner interest units held	[3]	233,856,623			233,856,623
Series A Preferred Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Preferred Units Held	[3],[7]	14,520,000			14,520,000
Transitional Service [Member] | Enable Midstream Partners [Member]
Related Party Transaction, Other Revenues from Transactions with Related Party	[8]	$ 1		0	$ 4		3
Transactions with Enable [Abstract]
Accounts receivable for amounts billed for transition services (CenterPoint Energy)		3			3				1
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Transactions with Enable [Abstract]
Natural gas expenses, including transportation and storage costs (CenterPoint Energy and CERC)		23		23	89		80
Accounts payable for natural gas purchases from Enable (CenterPoint Energy and CERC)		$ 8			$ 8				13
Enable Midstream Partners [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[2]				100.00%
Enable Units [Abstract]
Maximum incentive distribution right					50.00%
Enable Midstream Partners [Member] | OGE [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[2]				25.60%
Enable Midstream Partners [Member] | Public unitholders [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[2]				20.40%
Enable Midstream Partners [Member] | Minimum [Member]
Enable Units [Abstract]
Incentive distribution per unit					$ 0.2875
Enable Midstream Partners [Member] | Maximum [Member]
Enable Units [Abstract]
Incentive distribution per unit					$ 0.330625
Enable Midstream Partners [Member] | Common Units [Member]
Enable Units [Abstract]
Limited partner interest units held		433,216,156			433,216,156
Enable Midstream Partners [Member] | Common Units [Member] | OGE [Member]
Enable Units [Abstract]
Limited partner interest units held		110,982,805			110,982,805
Enable Midstream Partners [Member] | Common Units [Member] | Public unitholders [Member]
Enable Units [Abstract]
Limited partner interest units held		88,376,728			88,376,728
Enable GP, LLC [Member] | CenterPoint Energy [Member]
Enable Units [Abstract]
Management rights ownership percentage	[9],[10]				50.00%
Incentive distribution right	[10],[11]				40.00%
Enable GP, LLC [Member] | OGE [Member]
Enable Units [Abstract]
Management rights ownership percentage	[9]				50.00%
Incentive distribution right	[11]				60.00%
Enable Midstream Partners [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | CERC Corp [Member]
Investment in unconsolidated affiliate - discontinued operations		$ 0	[12]		$ 0	[12]		$ 2,400	$ 2,472	[12]
Deferred income taxes, net - discontinued operations								$ 974
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Equity in earnings of unconsolidated affiliate, net		57		68	184		199
Income tax expense		13		26	44		75
Income from discontinued operations (net of tax of $13, $26, $44 and $75, respectively)		$ 44		$ 42	$ 140		$ 124
Common Units [Member] | Enable Midstream Partners [Member]
Enable Distributions [Abstract]
Enable common units distributions paid (per unit)		$ 0.318			$ 0.954
Series A Preferred Units [Member] | Enable Midstream Partners [Member]
Enable Distributions [Abstract]
Enable common units distributions paid (per unit)		$ 0.625			$ 1.875

[1] On September 4, 2018, CERC completed the Internal Spin. After such date, CNP Midstream owned the Enable common units previously owned by CERC.

[2] Excludes the Enable Series A Preferred Units owned by CenterPoint Energy.

[3] Includes Enable Series A Preferred Units held directly by CenterPoint Energy and common units held indirectly through CNP Midstream.

[4] Equity in earnings of unconsolidated affiliate includes CenterPoint Energy’s share of Enable’s earnings adjusted for the amortization of the basis difference of CenterPoint Energy’s original investment in Enable and their underlying equity in Enable’s net assets. The basis difference is amortized over approximately 31 years, the average life of the assets to which the basis difference is attributed.

[5] Reflects cash distributions of $0.318 and $0.954 per common unit for the three and nine months ended September 30, 2018 and 2017, respectively.

[6] Reflects cash distributions of $0.625 and $1.875 per Enable Series A Preferred Unit for the three and nine months ended September 30, 2018 and 2017, respectively.

[7] The carrying amount of the Enable Series A Preferred Units, reflected as Preferred units - unconsolidated affiliate on CenterPoint Energy’s Condensed Consolidated Balance Sheets, was $363 million as of both September 30, 2018 and December 31, 2017. No impairment charges or adjustment due to observable price changes were made during the current or prior reporting periods. See Note 2 for further discussion.

[8] Represents amounts billed under the Transition Agreements for certain support services provided to Enable. Actual transition services costs are recorded net of reimbursement.

[9] Enable is controlled jointly by CenterPoint Energy and OGE. Sale of CenterPoint Energy’s or OGE’s ownership interests in Enable GP to a third party is subject to mutual rights of first offer and first refusal, and CenterPoint Energy is not permitted to dispose of less than all of its interest in Enable GP.

[10] Includes interests held through CNP Midstream.

[11] Enable is expected to pay a minimum quarterly distribution of $0.2875 per common unit on its outstanding common units to the extent it has sufficient cash from operations after establishment of cash reserves and payment of fees and expenses, including payments to Enable GP and its affiliates, within 60 days after the end of each quarter. If cash distributions to Enable’s unitholders exceed $0.330625 per common unit in any quarter, Enable GP will receive increasing percentages or incentive distributions rights, up to 50%, of the cash Enable distributes in excess of that amount. In certain circumstances Enable GP will have the right to reset the minimum quarterly distribution and the target distribution levels at which the incentive distributions receive increasing percentages to higher levels based on Enable’s cash distributions at the time of the exercise of this reset election. To date, no incentive distributions have been made.

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