Derivative Instruments (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) Bcf		Dec. 31, 2014 USD ($) Bcf		Dec. 31, 2013 USD ($)
Weather Hedges Term		10 years
Derivative Asset, Fair Value, Gross Asset		$ 140		$ 149
Derivative Liability, Fair Value, Gross Liability		87		102
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		29		46		$ 21
Total fair value of derivative instruments that contain credit risk contingent features that are in a net liability position		3		2
Aggregate fair value of assets already posted as collateral		0		0
Credit risk contingent feature assets		2		2
Credit Risk Derivative Assets, at Fair Value		$ 125		$ 131
Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		767		804
Derivative Assets (Liabilities), at Fair Value, Net	[1]	$ 109		$ 111
Collateral Netting		56		64
Derivative, Fair Value, Net	[2]	53		47
Derivative, fair value, offsets, net		56		64
Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[2]	100		115
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(11)		(16)
Derivative Asset	[1]	89		99
Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[2]	40		34
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(4)		(2)
Derivative Asset	[1]	36		32
Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[2]	(62)		(84)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		51		65
Derivative Liability	[1]	(11)		(19)
Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[2]	(25)		(18)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		20		17
Derivative Liability	[1]	(5)		(1)
Gains (Losses) in Revenue [Member] | Weather Hedge Swaps [Member]
Derivative, Gain (Loss) on Derivative, Net		(4)		(10)		(16)
Gains (Losses) in Revenue [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		134		35		11
Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	[3]	(105)		11		$ 10
Not Designated as Hedging Instrument [Member] | Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	90	[5],[6]	101	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	2	[5],[6]	1	[7],[8]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	36	[5],[6]	32	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	0	[5],[6]	0	[7],[8]
Not Designated as Hedging Instrument [Member] | Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	10	[5],[6]	14	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	60	[5],[6]	83	[7],[8]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	4	[5],[6]	2	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	$ 25	[5],[6]	$ 18	[7],[8]
Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		112		60
Swap [Member] | Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		133		127
Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9]	$ 115		$ 127
Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value		0		0
Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value		10		4
2014To2015 [Member]
Weather Hedge, Bilateral Cap Amount		16
2013To2014 [Member]
Weather Hedge, Bilateral Cap Amount		16
Enable Midstream Partners [Member] | Forward Contracts [Member] | Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		0		2
External Credit Rating, Investment Grade [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	6		4
External Credit Rating, Investment Grade [Member] | Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9],[10]	2		2
External Credit Rating, Investment Grade [Member] | Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	0		0
External Credit Rating, Investment Grade [Member] | Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	$ 4		$ 2

[1] 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.

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

[3] The Gains (Losses) in Expense: Natural Gas includes $-0- and $2 million during the years ended December 31, 2015 and 2014, respectively, related to physical forwards purchased from Enable.

[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. 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 offset by collateral netting of $56 million.

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

[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 $111 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, offset by collateral netting of $64 million.

[8] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 804 Bcf or a net 60 Bcf long position. Of the net long position, basis swaps constitute 127 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.