Derivative Instruments (Details)		12 Months Ended
		Dec. 31, 2016 USD ($) Bcf		Dec. 31, 2015 USD ($) Bcf		Dec. 31, 2014 USD ($)
Weather Hedges Term		10 years
Derivative Asset, Fair Value, Gross Asset		$ 105,000,000		$ 140,000,000
Derivative Liability, Fair Value, Gross Liability		67,000,000		87,000,000
Collateral posted (held), net		(14,000,000)		56,000,000
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		52,000,000		29,000,000		$ 46,000,000
Total fair value of derivative instruments that contain credit risk contingent features that are in a net liability position		1,000,000		3,000,000
Aggregate fair value of assets already posted as collateral		0		0
Credit risk contingent feature assets		0		2,000,000
Credit Risk Derivative Assets, at Fair Value		84,000,000	[1]	125,000,000
Weather Hedge Swap | Gains (Losses) in Revenue [Member]
Derivative, Gain (Loss) on Derivative, Net		$ 0		$ (4,000,000)		(10,000,000)
Natural gas derivative
Derivative, Nonmonetary Notional Amount, Volume | Bcf		1,035		767
Derivative Assets (Liabilities), at Fair Value, Net	[2]	$ 24,000,000		$ 109,000,000
Derivative, Fair Value, Net	[3]	38,000,000		53,000,000
Collateral posted (held), net		(14,000,000)		56,000,000
Natural gas derivative | Current Assets [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[3]	81,000,000		100,000,000
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(30,000,000)		(11,000,000)
Derivative Asset	[2]	51,000,000		89,000,000
Natural gas derivative | Other Noncurrent Assets [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[3]	24,000,000		40,000,000
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(5,000,000)		(4,000,000)
Derivative Asset	[2]	19,000,000		36,000,000
Natural gas derivative | Current Liabilities [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[3]	(57,000,000)		(62,000,000)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		16,000,000		51,000,000
Derivative Liability	[2]	(41,000,000)		(11,000,000)
Natural gas derivative | Other Noncurrent Liabilities [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[3]	(10,000,000)		(25,000,000)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		5,000,000		20,000,000
Derivative Liability	[2]	(5,000,000)		(5,000,000)
Natural gas derivative | Gains (Losses) in Revenue [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		(18,000,000)		134,000,000		35,000,000
Natural gas derivative | Gains (Losses) in Expense: Natural Gas [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		70,000,000		(105,000,000)		$ 11,000,000
Natural gas derivative | Not Designated as Hedging Instrument [Member] | Current Assets [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	79,000,000	[5],[6]	90,000,000	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	14,000,000	[5],[6]	2,000,000	[7],[8]
Natural gas derivative | Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	24,000,000	[5],[6]	36,000,000	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	5,000,000	[5],[6]	0	[7],[8]
Natural gas derivative | Not Designated as Hedging Instrument [Member] | Current Liabilities [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	2,000,000	[5],[6]	10,000,000	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	43,000,000	[5],[6]	60,000,000	[7],[8]
Natural gas derivative | Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	0	[5],[6]	4,000,000	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	$ 5,000,000	[5],[6]	$ 25,000,000	[7],[8]
Natural gas derivative | Long [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		59		112
Credit Risk Contract [Member]
Derivative Assets (Liabilities), at Fair Value, Net		$ 70,000,000		$ 125,000,000
Collateral posted (held), net		(14,000,000)		0
Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9]	47,000,000		115,000,000
Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value		33,000,000		0
Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value		4,000,000		10,000,000
2014To2015 [Member]
Weather Hedge, Bilateral Cap Amount		16,000,000
External Credit Rating, Investment Grade [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	36,000,000		6,000,000
External Credit Rating, Investment Grade [Member] | Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9],[10]	2,000,000		2,000,000
External Credit Rating, Investment Grade [Member] | Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	33,000,000		0
External Credit Rating, Investment Grade [Member] | Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	$ 1,000,000		$ 4,000,000
Swap [Member] | Natural gas derivative | Long [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		126		133

[1] The net of total non-trading natural gas derivative assets was $70 million and $125 million as of December 31, 2016 and 2015, respectively, as shown on CERC’s Consolidated Balance Sheets, and was comprised of the natural gas contracts derivatives assets separately shown above, impacted by collateral netting of $14 million and $-0- as of December 31, 2016 and 2015, respectively.

[2] The derivative assets and liabilities on the 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 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 Consolidated Balance Sheets. The net of total non-trading natural gas derivative assets and liabilities was a $24 million asset as shown on CERC’s 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 $14 million.

[6] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 1,035 Bcf or a net 59 Bcf long position. Of the net long position, basis swaps constitute a net 126 Bcf long position.

[7] Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts 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 Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $109 million asset as shown on CERC’s 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 $56 million.

[8] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 767 Bcf or a net 112 Bcf long position. Of the net long position, basis swaps constitute 133 Bcf.

[9] End users are comprised primarily of customers who have contracted to fix the price of a portion of their physical gas requirements for future periods.

[10] “Investment grade” is primarily determined using publicly available credit ratings, and considers credit support (including parent company guarantees) and collateral (including cash and standby letters of credit). For unrated counterparties, CERC determines a synthetic credit rating by performing financial statement analysis, and considers contractual rights and restrictions and collateral.