Derivative Instruments Derivative Fair Values (Details) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Bcf	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Bcf
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		$ 160		$ 160		$ 218
Derivative Liabilities Fair Value		751		751		775
Gain (loss) on derivative instruments not designated as hedging instruments		(252)	$ 14	(282)	$ 27
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
Gains (Losses) in Non-utility natural gas expense [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge		(12)	(4)	(14)	(14)
Gain (loss) on fair value hedges recognized in earnings	[1]	1	(1)	$ (1)	(2)
Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				1,862		1,795
Net amount presented in the consolidated balance sheets	[2]	82		$ 82		$ 130
Gross Amounts Recognized	[3]	50		50		111
Gross Amounts Offset in the Consolidated Balance Sheets		32		32		19
Energy Related Derivative [Member] | Gains (Losses) in Non-utility natural gas expense [Member]
Derivatives, Fair Value [Line Items]
Change in unrealized gain (loss) on fair value hedging instruments		13	3	13	12
Energy Related Derivative [Member] | Current Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	99		99		165
Gross Amounts Offset		(25)		(25)		(55)
Derivative Asset	[2]	74		74		110
Energy Related Derivative [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	61		61		53
Gross Amounts Offset		(15)		(15)		(9)
Derivative Asset	[2]	46		46		44
Energy Related Derivative [Member] | Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(69)		(69)		(83)
Gross Amounts Offset		43		43		63
Derivative Liability	[2]	(26)		(26)		(20)
Energy Related Derivative [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts Recognized	[3]	(41)		(41)		(24)
Gross Amounts Offset		29		29		20
Derivative Liability	[2]	(12)		$ (12)		$ (4)
Energy Related Derivative [Member] | Long [Member]
Derivatives, Fair Value [Line Items]
Derivative gross volume notional amount (in Bcf) | Bcf				268		224
IDS Derivative [Member] | Gains (losses) in Other Income (Expense) [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		(254)	(13)	$ (272)	(23)
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		641		641		668
CERC Corp [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets Fair Value		160		160		218
Derivative Liabilities Fair Value		110		110		107
Gain (loss) on derivative instruments not designated as hedging instruments		2	27	(10)	50
CERC Corp [Member] | Energy Related Derivative [Member] | Gains (Losses) in Non-utility revenues [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		11	36	68	132
CERC Corp [Member] | Energy Related Derivative [Member] | Gains (Losses) in Non-utility natural gas expense [Member]
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative instruments not designated as hedging instruments		(9)	$ (9)	(78)	$ (82)
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	[4],[5],[6]	0		0		13
Derivative Liabilities Fair Value	[4],[5],[6]	3		3		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	[4],[5],[6]	76		76		114
Derivative Liabilities Fair Value	[4],[5],[6]	2		2		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	[4],[5],[6]	46		46		44
Derivative Liabilities Fair Value	[4],[5],[6]	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	[4],[5],[6]	23		23		38
Derivative Liabilities Fair Value	[4],[5],[6]	64		64		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	[4],[5],[6]	15		15		9
Derivative Liabilities Fair Value	[4],[5],[6]	$ 41		$ 41		$ 24

[1] Hedge ineffectiveness results from the basis ineffectiveness discussed above, and excludes the impact to natural gas expense from timing ineffectiveness. Timing ineffectiveness arises due to changes in the 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. As the commodity contract nears the settlement date, spot-to-forward price differences should converge, which should reduce or eliminate the impact of this ineffectiveness on natural gas expense.

[2] 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.

[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 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 $82 million asset and a $130 million asset as of June 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 table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above, impacted by collateral netting of $32 million and $19 million, respectively.

[6] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 1,862 Bcf or a net 268 Bcf long position and 1,795 Bcf or a net 224 Bcf long position as of June 30, 2018 and December 31, 2017, respectively. Certain natural gas contracts hedge basis risk only and lack a fixed price exposure.