Derivative Instruments Summary of Derivative Activity (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Bcf	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Bcf
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		$ 277		$ 277		$ 220
Derivative Liabilities Fair Value		1,057		1,057		833
Derivative Asset		42		42		57
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		(7)		(7)		1
Total amounts presented in the statements of income in which the effects of hedges are recorded	[1]	852	$ 864	3,013	$ 2,927
Gain (loss) on derivative instruments not designated as hedging instruments		7	(42)	(57)	(246)
Aggregate fair value of derivatives containing material adverse change provisions in a net liability position		1		1		1
Fair value of collateral already posted		0		0		0
Additional collateral required to be posted if credit risk contingent features triggered		1		1		0
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		0		0		0
Derivative Liabilities Fair Value		15		$ 15		$ 0
Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				2,252		1,674
Net amount presented in the consolidated balance sheets	[2]	102		$ 102		$ 31
Gross Amounts Recognized	[3]	52		52		12
Gross Amounts Offset in the Consolidated Balance Sheets		50		50		19
Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	120		120		100
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		(7)		(7)		1
Gross Amounts Recognized	[3]	199		199		166
Gross Amounts Offset		(79)		(79)		(66)
Energy Related Derivative [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	64		64		38
Gross Amounts Recognized	[3]	78		78		54
Gross Amounts Offset		(14)		(14)		(16)
Energy Related Derivative [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(157)		(157)		(183)
Gross Amounts Offset		107		107		81
Derivative Liability	[2]	(50)		(50)		(102)
Energy Related Derivative [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(68)		(68)		(25)
Gross Amounts Offset		36		36		20
Derivative Liability	[2]	(32)		(32)		(5)
Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[4],[5],[6]	123		123		103
Derivative Liabilities Fair Value	[4],[5],[6]	3		3		3
Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[4],[5],[6]	65		65		38
Derivative Liabilities Fair Value	[4],[5],[6]	0		0		0
Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[4],[5],[6]	69		69		62
Derivative Liabilities Fair Value	[4],[5],[6]	154		154		173
Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[4],[5],[6]	13		13		16
Derivative Liabilities Fair Value	[4],[5],[6]	68		$ 68		$ 25
Energy Related Derivative [Member] | Long [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				374		140
IDS Derivative [Member] | Not Designated as Hedging Instrument [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		0		$ 0		$ 0
Derivative Liabilities Fair Value		817		817		601
Houston Electric [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		0		0		0
Derivative Liabilities Fair Value		0		0		24
CERC Corp [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		277		277		220
Derivative Liabilities Fair Value		205		205		208
Derivative Asset		42		42		57
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		(7)		(7)		1
Total amounts presented in the statements of income in which the effects of hedges are recorded	[1]	687	864	2,627	2,927
Gain (loss) on derivative instruments not designated as hedging instruments		69	2	159	70
Aggregate fair value of derivatives containing material adverse change provisions in a net liability position		1		1		1
Fair value of collateral already posted		0		0		0
Additional collateral required to be posted if credit risk contingent features triggered		1		$ 1		$ 0
CERC Corp [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				2,252		1,674
Net amount presented in the consolidated balance sheets	[2]	122		$ 122		$ 31
Gross Amounts Recognized	[3]	72		72		12
Gross Amounts Offset in the Consolidated Balance Sheets		50		50		19
CERC Corp [Member] | Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	120		120		100
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		(7)		(7)		1
Gross Amounts Recognized	[3]	199		199		166
Gross Amounts Offset		(79)		(79)		(66)
CERC Corp [Member] | Energy Related Derivative [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	64		64		38
Gross Amounts Recognized	[3]	78		78		54
Gross Amounts Offset		(14)		(14)		(16)
CERC Corp [Member] | Energy Related Derivative [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(151)		(151)		(183)
Gross Amounts Offset		107		107		81
Derivative Liability	[2]	(44)		(44)		(102)
CERC Corp [Member] | Energy Related Derivative [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(54)		(54)		(25)
Gross Amounts Offset		36		36		20
Derivative Liability	[2]	(18)		(18)		(5)
CERC Corp [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[7],[8],[9]	123		123		103
Derivative Liabilities Fair Value	[7],[8],[9]	3		3		3
CERC Corp [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[7],[8],[9]	65		65		38
Derivative Liabilities Fair Value	[7],[8],[9]	0		0		0
CERC Corp [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[7],[8],[9]	69		69		62
Derivative Liabilities Fair Value	[7],[8],[9]	148		148		173
CERC Corp [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[7],[8],[9]	13		13		16
Derivative Liabilities Fair Value	[7],[8],[9]	54		$ 54		$ 25
CERC Corp [Member] | Energy Related Derivative [Member] | Long [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				374		140
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Fair Value Hedge [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		0		$ 0		$ 0
Derivative Liabilities Fair Value		0		0		24
Cash Flow Hedging [Member] | Houston Electric [Member] | Interest Rate Contract [Member] | Designated as Fair Value Hedge [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		0		0		0
Derivative Liabilities Fair Value		0		0		24
Fair Value Hedging [Member] | Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		42		42		57
Fair Value Hedging [Member] | Energy Related Derivative [Member] | Designated as Fair Value Hedge [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[4],[5],[6]	7		7		1
Derivative Liabilities Fair Value	[4],[5],[6]	0		0		7
Fair Value Hedging [Member] | CERC Corp [Member] | Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		42		42		57
Fair Value Hedging [Member] | CERC Corp [Member] | Energy Related Derivative [Member] | Designated as Fair Value Hedge [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value	[7],[8],[9]	7		7		1
Derivative Liabilities Fair Value	[7],[8],[9]	0		0		$ 7
Gains (Losses) in Revenue [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		69	2	159	70
Gains (Losses) in Revenue [Member] | CERC Corp [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		69	2	159	70
Non-utility Natural Gas Expense [Member] | Fair Value Hedging [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on fair value hedging instruments	[1]	2	1	(8)	(13)
Amounts excluded from effectiveness testing recognized in earnings immediately	[1]	(59)	6	(138)	(73)
Non-utility Natural Gas Expense [Member] | Fair Value Hedging [Member] | Energy Related Derivative [Member] | Designated as Fair Value Hedge [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on fair value hedging instruments	[1]	(2)	(1)	8	13
Non-utility Natural Gas Expense [Member] | Fair Value Hedging [Member] | CERC Corp [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on fair value hedging instruments	[1]	2	1	(8)	(13)
Amounts excluded from effectiveness testing recognized in earnings immediately	[1]	(59)	6	(138)	(73)
Non-utility Natural Gas Expense [Member] | Fair Value Hedging [Member] | CERC Corp [Member] | Energy Related Derivative [Member] | Designated as Fair Value Hedge [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on fair value hedging instruments	[1]	(2)	(1)	8	13
Gains (Losses) in Other Income (Expense) [Member] | IDS Derivative [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		$ (62)	$ (44)	$ (216)	$ (316)

[1] Income statement impact associated with cash flow hedge activity is related to gains and losses reclassified from Accumulated other comprehensive income into income. Amounts are immaterial for each Registrant in the three and nine months ended September 30, 2019 and 2018, respectively.

[2] The derivative assets and liabilities on the Registrant’s respective Condensed Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default.

[3] Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements.

[4] Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable.

[5] Natural gas contracts are presented on a net basis in CenterPoint Energy’s Condensed Consolidated Balance Sheets as they are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within CenterPoint Energy’s Condensed Consolidated Balance Sheets. The net of total non-trading natural gas derivative assets and liabilities is detailed in the Offsetting of Natural Gas Derivative Assets and Liabilities table below.

[6] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 2,252 Bcf or a net 374 Bcf long position and 1,674 Bcf or a net 140 Bcf long position as of September 30, 2019 and December 31, 2018, respectively. Certain natural gas contracts hedge basis risk only and lack a fixed price exposure.

[7] Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable.

[8] Natural gas contracts are presented on a net basis in CERC’s Condensed Consolidated Balance Sheets as they are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within CERC’s Condensed Consolidated Balance Sheets. The net of total non-trading natural gas derivative assets and liabilities is detailed in the Offsetting of Natural Gas Derivative Assets and Liabilities table below.

[9] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 2,252 Bcf or a net 374 Bcf long position and 1,674 Bcf or a net 140 Bcf long position as of September 30, 2019 and December 31, 2018, respectively. Certain natural gas contracts hedge basis risk only and lack a fixed price exposure.