Unconsolidated Affiliate (CenterPoint Energy and CERC) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	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		84	$ 84	$ 167	$ 167
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract]
CenterPoint Energy’s and CERC’s equity in earnings, net		58	59	127	131
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s and CERC’s equity method investment in Enable		2,451		2,451		2,472
CERC Corp [Member]
Enable Distributions [Abstract]
Total distributions received from Enable		75	75	149	149
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract]
CenterPoint Energy’s and CERC’s equity in earnings, net		58	59	127	131
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s and CERC’s equity method investment in Enable		$ 2,451		$ 2,451		2,472
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		54.00%		54.00%
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract]
Operating revenues		$ 805	626	$ 1,553	1,292
Cost of sales, excluding depreciation and amortization		444	279	819	587
Operating income		126	122	265	262
Net income attributable to Enable		86	86	191	197
CenterPoint Energy’s and CERC’s interest		46	47	103	107
Basis difference amortization (1)	[1]	12	12	24	24
CenterPoint Energy’s and CERC’s equity in earnings, net		58	59	$ 127	131
Basis difference amortization period				31 years
Equity Method Investment, Summarized Financial Information, Assets and Liabilities [Abstract]
Current assets		432		$ 432		416
Non-current assets		11,360		11,360		11,177
Current liabilities		1,258		1,258		1,279
Non-current liabilities		2,963		2,963		2,660
Non-controlling interest		11		11		12
Preferred equity		362		362		362
Enable partners’ equity		7,198		7,198		7,280
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CenterPoint Energy’s and CERC’s ownership interest in Enable partners’ equity		3,887		3,887		3,935
CenterPoint Energy’s and CERC’s basis difference		(1,436)		(1,436)		(1,463)
CenterPoint Energy’s and CERC’s equity method investment in Enable		2,451		2,451		2,472
Enable Midstream Partners [Member] | Common Units [Member]
Enable Distributions [Abstract]
Distributions received from Enable equity method investment		75	75	149	149
Enable Midstream Partners [Member] | Series A Preferred Units [Member]
Enable Distributions [Abstract]
Distributions received from Enable cost method investment		$ 9	9	$ 18	18
Enable Midstream Partners [Member] | CERC Corp [Member]
Enable Partnership Interest [Abstract]
Ownership percentage of equity method investment	[2]	54.00%		54.00%
Enable Midstream Partners [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[2]			100.00%
Enable Distributions [Abstract]
Maximum incentive distribution right				50.00%
Enable Midstream Partners [Member] | CERC Corp [Member]
Enable Units [Abstract]
Management rights ownership percentage				50.00%
Enable Distributions [Abstract]
Incentive distribution right				40.00%
Enable Midstream Partners [Member] | OGE [Member]
Enable Partnership Interest [Abstract]
Limited partner ownership interest	[2]			25.60%
Enable Units [Abstract]
Management rights ownership percentage				50.00%
Enable Distributions [Abstract]
Incentive distribution right				60.00%
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 Distributions [Abstract]
Incentive distribution per unit				$ 0.2875
Enable Midstream Partners [Member] | Maximum [Member]
Enable Distributions [Abstract]
Incentive distribution per unit				$ 0.330625
Common Units [Member] | Enable Midstream Partners [Member] | CERC Corp [Member]
Enable Units [Abstract]
Limited partner interest units held		233,856,623		233,856,623
Common Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Limited partner interest units held		433,064,636		433,064,636
Common Units [Member] | Enable Midstream Partners [Member] | OGE [Member]
Enable Units [Abstract]
Limited partner interest units held		110,982,805		110,982,805
Common Units [Member] | Enable Midstream Partners [Member] | Public unitholders [Member]
Enable Units [Abstract]
Limited partner interest units held		88,225,208		88,225,208
Series A Preferred Units [Member] | Enable Midstream Partners [Member]
Enable Units [Abstract]
Preferred Units Held	[3]	14,520,000		14,520,000
Transitional Service [Member] | Enable Midstream Partners [Member]
Transactions with Enable [Abstract]
Reimbursement of transition services (1)	[4]	$ 1	1	$ 3	3
Accounts receivable for amounts billed for transition services		3		3		1
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Transactions with Enable [Abstract]
Natural gas expenses, including transportation and storage costs		29	$ 24	66	$ 57
Accounts payable for natural gas purchases from Enable		$ 8		$ 8		$ 13

[1] Equity in earnings of unconsolidated affiliate includes CenterPoint Energy’s and CERC’s share of Enable’s earnings adjusted for the amortization of the basis difference of CenterPoint Energy’s and CERC’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.

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

[3] The carrying amount of the Series A Preferred Units, reflected as Preferred units - unconsolidated affiliate on CenterPoint Energy’s Condensed Consolidated Balance Sheets, was $363 million as of both June 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.

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