Short-Term Borrowings and Long-term Debt (Details)				6 Months Ended
		Mar. 26, 2018 USD ($)	Feb. 28, 2018 USD ($)	Jun. 30, 2018 USD ($)		Dec. 31, 2017 USD ($)
Short-term Debt [Line Items]
Short-term borrowings				$ 0		$ 39,000,000
Line of Credit Facility [Abstract]
Size of credit facility				2,900,000,000		2,900,000,000
Parent Company [Member]
Line of Credit Facility [Abstract]
Size of credit facility				1,700,000,000	[1]	1,700,000,000
Temporary increased line of credit facility, maximum borrowing capacity				3,300,000,000
Houston Electric [Member]
Line of Credit Facility [Abstract]
Size of credit facility				300,000,000		300,000,000
General mortgage bonds used as collateral				118,000,000		118,000,000
CERC Corp [Member]
Short-term Debt [Line Items]
Short-term borrowings				0		39,000,000
Line of Credit Facility [Abstract]
Size of credit facility				900,000,000		900,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				0		0
Revolving Credit Facility [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Long-term line of credit	[2]			0		0
Revolving Credit Facility [Member] | Houston Electric [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				0		0
Revolving Credit Facility [Member] | CERC Corp [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				$ 0		0
Line of Credit [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Percentage on limitation of debt to total capitalization under covenant				65.00%
Percentage on limitation of debt to total capitalization under covenant amended (in hundredths)				70.00%
Ratio of indebtedness to net capital	[3]			0.521
System restoration costs threshold for increase in permitted debt to EBITDA covenant ratio				$ 100,000,000
Consecutive period for system restoration costs to exceed $100 million (in months)				12
Line of Credit [Member] | Parent Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Abstract]
Basis spread on LIBOR	[4]			1.25%
Line of Credit [Member] | Houston Electric [Member]
Line of Credit Facility [Abstract]
Percentage on limitation of debt to total capitalization under covenant	[5]			65.00%
Ratio of indebtedness to net capital	[3]			0.507
Line of Credit [Member] | Houston Electric [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Abstract]
Basis spread on LIBOR	[4]			1.125%
Line of Credit [Member] | CERC Corp [Member]
Line of Credit Facility [Abstract]
Percentage on limitation of debt to total capitalization under covenant				65.00%
Ratio of indebtedness to net capital	[3]			0.378
Line of Credit [Member] | CERC Corp [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Abstract]
Basis spread on LIBOR	[4]			1.25%
Letter of Credit [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				$ 11,000,000		11,000,000
Letter of Credit [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Long-term line of credit	[2]			6,000,000		6,000,000
Letter of Credit [Member] | Houston Electric [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				4,000,000		4,000,000
Letter of Credit [Member] | CERC Corp [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				1,000,000		1,000,000
Commercial Paper [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				565,000,000		1,753,000,000
Commercial Paper [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Long-term line of credit	[2]			$ 0		$ 855,000,000
Weighted average interest rate of debt	[2]			0.00%		1.88%
Commercial Paper [Member] | Houston Electric [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				$ 0		$ 0
Commercial Paper [Member] | CERC Corp [Member]
Line of Credit Facility [Abstract]
Long-term line of credit				$ 565,000,000		$ 898,000,000
Weighted average interest rate of debt				2.37%		1.72%
General Mortgage Bonds Due 2048 [Member] | Houston Electric [Member]
Debt Instruments [Abstract]
Principal amount of debt issued			$ 400,000,000
Interest rate of debt issued			3.95%
Maturity date of debt issued			Mar. 01, 2048
Senior Notes Due 2023 [Member] | CERC Corp [Member]
Debt Instruments [Abstract]
Principal amount of debt issued		$ 300,000,000
Interest rate of debt issued		3.55%
Maturity date of debt issued		Apr. 01, 2023
Senior Notes Due 2028 [Member]
Debt Instruments [Abstract]
Principal amount of debt issued		$ 300,000,000
Interest rate of debt issued		4.00%
Maturity date of debt issued		Apr. 01, 2028
Product Financing Arrangement [Member]
Short-term Debt [Line Items]
Short-term borrowings				$ 0		$ 39,000,000
Merger Agreement with Vectren [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Temporary increased line of credit facility, maximum borrowing capacity				$ 3,300,000,000
Merger Agreement with Vectren [Member] | Line of Credit [Member] | Parent Company [Member]
Line of Credit Facility [Abstract]
Percentage on limitation of debt to total capitalization under covenant amended (in hundredths)	[5],[6]			75.00%

[1] Pursuant to the amendment entered into in May 2018, the aggregate commitments under the CenterPoint Energy revolving credit facility will increase to $3.3 billion upon the satisfaction of certain conditions described above.

[2] Pursuant to the amendment entered into in May 2018, the aggregate commitments under the CenterPoint Energy revolving credit facility will increase to $3.3 billion upon the satisfaction of certain conditions described above.

[3] As defined in the revolving credit facility agreement, excluding Securitization Bonds.

[4] Based on current credit ratings.

[5] For CenterPoint Energy (whenever its financial covenant limit is 65%) and Houston Electric, the financial covenant limit will temporarily increase from 65% to 70% if Houston Electric experiences damage from a natural disaster in its service territory and CenterPoint Energy certifies to the administrative agent that Houston Electric has incurred system restoration costs reasonably likely to exceed $100 million in a consecutive 12-month period, all or part of which Houston Electric intends to seek to recover through securitization financing. Such temporary increase in the financial covenant would be in effect from the date CenterPoint Energy delivers its certification until the earliest to occur of (i) the completion of the securitization financing, (ii) the first anniversary of CenterPoint Energy’s certification or (iii) the revocation of such certification.

[6] CenterPoint Energy’s financial covenant limit will return to 65% upon the earlier of (i) June 30, 2019 or (ii) the termination of all commitments in respect of the Bridge Facility without any borrowing thereunder.