Derivative Instruments Summary of Derivative Activity (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Bcf	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Bcf
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		$ 164		$ 164		$ 218
Derivative Liabilities Fair Value		795		795		775
Derivative Asset		39		39		80
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		1		1		14
Total amounts presented in the statements of income in which the effects of hedges are recorded	[1]	864	$ 832	2,927	$ 2,843
Gain (loss) on derivative instruments not designated as hedging instruments		(42)	(6)	(246)	103
Net deferred gain (loss) from cash flow hedges (net of tax)		3	(2)	6	(3)
Aggregate fair value of derivatives containing material adverse change provisions in a net liability position		2		2		2
Fair value of collateral already posted		0		0		0
Additional collateral required to be posted if credit risk contingent features triggered		1		1		2
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Net deferred gain (loss) from cash flow hedges (net of tax)	[2]	0	(1)	(1)	(1)
Interest Rate Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		1		$ 1		$ 1
Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				1,865		1,795
Net amount presented in the consolidated balance sheets	[3]	72		$ 72		$ 130
Gross Amounts Recognized	[4]	51		51		111
Gross Amounts Offset in the Consolidated Balance Sheets		21		21		19
Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[3]	73		73		110
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of Hedged Item		1		1		14
Gross Amounts Recognized	[4]	107		107		165
Gross Amounts Offset		(34)		(34)		(55)
Energy Related Derivative [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[3]	38		38		44
Gross Amounts Recognized	[4]	54		54		53
Gross Amounts Offset		(16)		(16)		(9)
Energy Related Derivative [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[4]	(77)		(77)		(83)
Gross Amounts Offset		44		44		63
Derivative Liability	[3]	(33)		(33)		(20)
Energy Related Derivative [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[4]	(33)		(33)		(24)
Gross Amounts Offset		27		27		20
Derivative Liability	[3]	(6)		$ (6)		$ (4)
Energy Related Derivative [Member] | Long [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				310		224
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		685		685		668
Houston Electric [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		3		3		0
Derivative Liabilities Fair Value		0		0		0
Net deferred gain (loss) from cash flow hedges (net of tax)		3	0	7	(1)
Houston Electric [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Net deferred gain (loss) from cash flow hedges (net of tax)	[2]	3	0	7	(1)
CERC Corp [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		161		161		218
Derivative Liabilities Fair Value		110		110		107
Total amounts presented in the statements of income in which the effects of hedges are recorded		864	832	2,927	2,843
Gain (loss) on derivative instruments not designated as hedging instruments		2	30	70	162
Net deferred gain (loss) from cash flow hedges (net of tax)		0	(1)	0	(1)
CERC Corp [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Net deferred gain (loss) from cash flow hedges (net of tax)	[2]	0	(1)	0	(1)
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	[5],[6],[7]	76		76		114
Derivative Liabilities Fair Value	[5],[6],[7]	3		3		4
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	[5],[6],[7]	38		38		44
Derivative Liabilities Fair Value	[5],[6],[7]	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	[5],[6],[7]	31		31		38
Derivative Liabilities Fair Value	[5],[6],[7]	72		72		78
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	[5],[6],[7]	16		16		9
Derivative Liabilities Fair Value	[5],[6],[7]	33		33		24
Cash Flow Hedging [Member] | Houston Electric [Member] | Interest Rate Contract [Member] | Designated as Fair Value Hedge [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		3		3		0
Derivative Liabilities Fair Value		0		0		0
Fair Value Hedging [Member] | Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		39		39		80
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	[5],[6],[7]	0		0		13
Derivative Liabilities Fair Value	[5],[6],[7]	2		2		$ 1
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		2	30	70	162
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]	1	4	(13)	(10)
Amounts excluded from effectiveness testing recognized in earnings immediately (1)	[1],[8]	6	(9)	(73)	(93)
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]	(1)	(4)	13	10
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		(44)	(36)	(316)	(59)
Gains (Losses) in Interest and other finance charges [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		0	0	0	0
Gains (Losses) in Interest and other finance charges [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) reclassified from accumulated OCI into income		$ 1	$ (1)	$ 1	$ (1)

[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 the Registrants for both the three and nine months ended September 30, 2018 and 2017, respectively.

[2] Gains and losses are reclassified from accumulated other comprehensive income into income when the hedged transactions affect earnings. The reclassification amounts are included in Interest and other finance charges in the Condensed Statements of Consolidated Income. Amounts are less than $1 million for each of the three and nine months ended September 30, 2018 and 2017. Over the next twelve months, estimated amortization of accumulated other comprehensive income into related income is expected to be immaterial.

[3] The derivative assets and liabilities on the 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.

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

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

[6] Natural gas contracts are presented on a net basis in the 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 the Condensed Consolidated Balance Sheets. The net of total non-trading natural gas derivative assets and liabilities was a $72 million asset and a $130 million asset as of September 30, 2018 and December 31, 2017, respectively, as shown on CenterPoint Energy’s and CERC’s Condensed Consolidated Balance Sheets (and as detailed in the Offsetting of Natural Gas Derivative Assets and Liabilities table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above, impacted by collateral netting of $21 million and $19 million, respectively.

[7] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 1,865 Bcf or a net 310 Bcf long position and 1,795 Bcf or a net 224 Bcf long position as of September 30, 2018 and December 31, 2017, respectively. Certain natural gas contracts hedge basis risk only and lack a fixed price exposure.

[8] As a result of the adoption of ASU 2017-12 effective January 1, 2018 (see Note 2 for additional information), CenterPoint Energy and CERC exclude from their assessment of hedge effectiveness the natural gas market price difference between locations of the hedged inventory and the delivery location specified in the hedge instruments. Prior to the adoption of this accounting guidance, the timing difference between the spot price and the futures price, as well as the difference between the timing of the settlement of the futures and the valuation of the underlying physical commodity, was excluded from the assessment of effectiveness for CenterPoint Energy’s and CERC’s existing fair value hedges and will continue to be excluded from the assessment of hedge effectiveness. CenterPoint Energy and CERC elected to continue to immediately recognize amounts excluded from hedge effectiveness in their respective Condensed Statements of Consolidated Income.