Unconsolidated Affiliate (CenterPoint Energy and CERC) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended	12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Sep. 04, 2018
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					$ 333	333		$ 319
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
CenterPoint Energy’s equity in earnings, net					307	265		208
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s equity method investment in Enable		2,482			2,482	2,472
CERC Corp [Member]
Investment in unconsolidated affiliates - discontinued operations		0			0	2,472
Deferred income taxes, net - discontinued operations		$ 0			0	927
Contribution from parent					960	38		72
Enable Distributions [Abstract]
Total distributions received from Enable					223	297		297
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Income tax expense					46	104		81
Income (loss) from discontinued operations, net of tax					$ 138	$ 161		127
Enable Midstream Partners [Member]
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Basis difference amortization period					30 years
OGE [Member]
Enable Units [Abstract]
Percentage of sales that trigger right of first refusal					5.00%
Enable Midstream Partners [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[1],[2]	54.00%			54.00%	54.10%
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Operating revenues					$ 3,431	$ 2,803		2,272
Cost of sales, excluding depreciation and amortization					1,819	1,381		1,017
Depreciation and amortization					398	366		338
Operating income					648	528		385
Net income attributable to Enable common units					485	400		290
CenterPoint Energy’s interest					262	216		160
Basis difference amortization (1)	[3]				47	49		48
Loss on dilution, net of proportional basis difference recognition					(2)	0		0
CenterPoint Energy’s equity in earnings, net	[4]				307	265		$ 208
Equity Method Investment, Summarized Financial Information [Abstract]
Current assets		$ 449			449	416
Non-current assets		11,995			11,995	11,177
Current liabilities		1,615			1,615	1,279
Non-current liabilities		3,211			3,211	2,660
Non-controlling interest		38			38	12
Preferred equity		362			362	362
Enable partners’ equity		7,218			7,218	7,280
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s ownership interest in Enable partners’ equity		3,896			3,896	3,935
CenterPoint Energy’s basis difference		(1,414)			(1,414)	(1,463)
CenterPoint Energy’s equity method investment in Enable		$ 2,482			$ 2,482	$ 2,472
Enable Midstream Partners [Member] | Common Units [Member]
Enable Distributions [Abstract]
Distribution per share of common units	[5]	$ 0.3180		$ 0.9540		$ 1.2720		$ 1.2720
Distributions received from equity method investment		$ 74	[5]	$ 223		$ 297		$ 297
Enable Midstream Partners [Member] | Series A Preferred Units [Member]
Enable Distributions [Abstract]
Distribution per share of Series A preferred units	[6]				$ 2.5000	$ 2.5000		$ 1.5417
Distributions received from Enable cost method investment	[6]				$ 36	$ 36		$ 22
Enable Midstream Partners [Member] | CERC Corp [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[1],[2]					54.10%
Enable Midstream Partners [Member] | CERC Corp [Member] | Common Units [Member]
Enable Distributions [Abstract]
Distribution per share of common units				$ 0.9540		$ 1.2720		$ 1.2720
Distributions received from equity method investment	[5]				$ 223	$ 297		$ 297
Common Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Limited partner interest units held	[2]	233,856,623			233,856,623	233,856,623
Common Units [Member] | Enable Midstream Partners [Member] | CERC Corp [Member]
Enable Units [Abstract]
Limited partner interest units held	[2]					233,856,623
Series A Preferred Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Preferred units held	[2],[7]	14,520,000			14,520,000	14,520,000
Enable Internal Spin [Member] | CERC Corp [Member]
Contribution from parent					$ 600
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Transaction with Enable [Abstract]
Natural gas expenses, including transportation and storage costs					122	$ 115		110
Accounts payable for natural gas purchases from Enable		$ 11			11	13
Natural Gas Expenses [Member] | Enable Midstream Partners [Member] | CERC Corp [Member]
Transaction with Enable [Abstract]
Natural gas expenses, including transportation and storage costs						115		110
Accounts payable for natural gas purchases from Enable						13
Transitional Service [Member] | Enable Midstream Partners [Member]
Transaction with Enable [Abstract]
Reimbursement of transition services (1)	[4]				4	4		7
Accounts receivable for amounts billed for transition services		$ 2			$ 2	$ 1
Enable Midstream Partners [Member]
Enable Units [Abstract]
Maximum incentive distribution right					50.00%
Enable Midstream Partners [Member] | OGE [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[1]				25.60%	25.70%
Enable Midstream Partners [Member] | Public unitholders [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[1]				20.40%	20.20%
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] | OGE [Member]
Enable Units [Abstract]
Limited partner interest units held		110,982,805			110,982,805	110,982,805
Enable Midstream Partners [Member] | Common Units [Member] | Public unitholders [Member]
Enable Units [Abstract]
Limited partner interest units held		88,392,983			88,392,983	87,744,652
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | Enable Midstream Partners [Member] | CERC Corp [Member]
Investment in unconsolidated affiliates - discontinued operations						$ 2,472	[8]	2,505	[8]	$ 2,400
Deferred income taxes, net - discontinued operations										$ 974
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Equity in earnings of unconsolidated affiliate, net					$ 184	265		208
Income tax expense					46	104		81
Income (loss) from discontinued operations, net of tax					$ 138	$ 161		$ 127
Enable GP, LLC [Member]
Enable Units [Abstract]
Management rights ownership percentage					50.00%
Incentive distribution right					40.00%
Enable GP, LLC [Member] | CERC Corp [Member]
Enable Units [Abstract]
Management rights ownership percentage	[9],[10]					50.00%
Incentive distribution right	[10],[11]					40.00%
Enable GP, LLC [Member] | CenterPoint Energy [Member]
Enable Units [Abstract]
Management rights ownership percentage	[9],[10]				50.00%	50.00%
Incentive distribution right	[10],[11]				40.00%	40.00%
Enable GP, LLC [Member] | OGE [Member]
Enable Units [Abstract]
Management rights ownership percentage	[9]				50.00%	50.00%
Incentive distribution right	[11]				60.00%	60.00%

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

[2] Prior to the Internal Spin on September 4, 2018 described above, CenterPoint Energy’s investment in Enable’s common units, excluding the Enable Series A Preferred Units held directly by CenterPoint Energy, was held indirectly through CERC.

[3] Equity in earnings of unconsolidated affiliate includes CenterPoint Energy’s share of Enable earnings adjusted for the amortization of the basis difference of CenterPoint Energy’s original investment in Enable and its underlying equity in net assets of Enable. The basis difference is being amortized over approximately 30 years, the remaining average life of the assets to which the basis difference is attributed.

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

[5] Reflects CERC’s ownership of Enable common units up to September 4, 2018 when CERC completed the Internal Spin. After such date, distributions from Enable were received directly by CenterPoint Energy.

[6] 2016 amounts represent the period from February 18, 2016 to December 31, 2016.

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

[8] On September 4, 2018, CERC completed the Internal Spin. For further information regarding the Internal Spin, see Note 11.

[9] As of December 31, 2018, 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] CenterPoint Energy held the management rights and incentive distributions rights in Enable GP indirectly through CERC until the Internal Spin on September 4, 2018 described above.

[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.