Fair Value Measurements (Details)		3 Months Ended			12 Months Ended
		Dec. 31, 2015 USD ($)		Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($)		Dec. 31, 2013 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		$ 0			$ 0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount		0			0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount		0			0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0			0
Assets
Derivative Asset, Fair Value, Gross Liability		(15,000,000)	[1]		(15,000,000)	[1]	$ (18,000,000)	[2]
Total assets		138,000,000			138,000,000		144,000,000
Liabilities
Derivative Liability, Fair Value, Gross Asset		(71,000,000)	[1]		(71,000,000)	[1]	(82,000,000)	[2]
Total liabilities		16,000,000			16,000,000		20,000,000
Cash collateral posted with counterparties		56,000,000			56,000,000		64,000,000
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance					17,000,000	[3]	3,000,000	[3]	$ 2,000,000
Total gains					7,000,000		14,000,000		3,000,000
Total settlements					(12,000,000)		1,000,000		(3,000,000)
Transfers out of Level 3					(1,000,000)		0		0
Transfers into Level 3					1,000,000		(1,000,000)		1,000,000
Ending balance (1)	[3]	12,000,000			12,000,000		17,000,000		3,000,000
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date					6,000,000		16,000,000		2,000,000
Carrying Amount [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Notes receivable - affiliated companies		363,000,000			363,000,000		363,000,000
Long-term debt		2,353,000,000			2,353,000,000		2,469,000,000
Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Notes receivable - affiliated companies		356,000,000			356,000,000		362,000,000
Long-term debt		2,551,000,000			2,551,000,000		2,772,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Total assets		17,000,000			17,000,000		20,000,000
Liabilities
Total liabilities		13,000,000			13,000,000		22,000,000
Significant Other Observable Inputs (Level 2) [Member]
Assets
Total assets		115,000,000			115,000,000		122,000,000
Liabilities
Total liabilities		65,000,000			65,000,000		77,000,000
Significant Unobservable Inputs (Level 3) [Member]
Assets
Total assets		21,000,000			21,000,000		20,000,000
Liabilities
Total liabilities		9,000,000			$ 9,000,000		3,000,000
Options Held [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Option volatilities low range					82.00%
Options Held [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Option volatilities low range					0.00%
Forward Contracts [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Illiquid forward price low range					3.29
Forward Contracts [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Illiquid forward price low range					1.36
Fair Value, Measurements, Recurring [Member]
Assets
Corporate equities		2,000,000			$ 2,000,000		2,000,000
Investments, including money market funds		11,000,000			11,000,000		11,000,000
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Corporate equities		2,000,000			2,000,000		2,000,000
Investments, including money market funds		11,000,000			11,000,000		11,000,000
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Corporate equities		0			0		0
Investments, including money market funds		0			0		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Corporate equities		0			0		0
Investments, including money market funds		0			0		0
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[4]	(15,000,000)	[1]		(15,000,000)	[1]	(18,000,000)	[2]
Natural gas derivatives (2)	[4]	125,000,000			125,000,000		131,000,000
Liabilities
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(71,000,000)	[1],[4]		(71,000,000)	[1],[4]	(82,000,000)	[2]
Natural gas derivatives (2)		16,000,000	[4]		16,000,000	[4]	20,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	4,000,000			4,000,000		7,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		13,000,000	[4]		13,000,000	[4]	22,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	115,000,000			115,000,000		122,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		65,000,000	[4]		65,000,000	[4]	77,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	21,000,000			21,000,000		20,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		9,000,000	[4]		9,000,000	[4]	3,000,000
Enable Midstream Partners [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Equity Method Investment, Other than Temporary Impairment		$ 975,000,000		$ 250,000,000	$ 1,225,000,000		$ 0		$ 0

[1] Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $56 million posted with the same counterparties.

[2] Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $64 million posted with the same counterparties.

[3] During 2015, 2014 and 2013, CenterPoint Energy did not have significant Level 3 purchases or sales.

[4] Natural gas derivatives include no material amounts related to physical forward transactions with Enable.