Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Weather Hedges Term	10
Derivative Asset, Fair Value, Gross Asset	$ 149		$ 43
Derivative Liability, Fair Value, Gross Liability	102		30
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	46		21		(20)
Total fair value of derivative instruments that contain credit risk contingent features that are in a net liability position	2		1
Aggregate fair value of assets already posted as collateral	1		1
Credit risk contingent feature assets	2		1
Credit Risk Derivative Assets, at Fair Value	131		34
Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume	804,000		607,000
Derivative Assets (Liabilities), at Fair Value, Net	111	[1]	13	[1]
Collateral Netting	64		1
Derivative, Fair Value, Net	47	[2]	13	[2]
Derivative, fair value, offsets, net	64		0
Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	115	[2]	32	[2]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(16)		(8)
Derivative Asset	99	[1]	24	[1]
Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	34	[2]	11	[2]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(2)		(1)
Derivative Asset	32	[1]	10	[1]
Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(84)	[2]	(25)	[2]
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	65		8
Derivative Liability	(19)	[1]	(17)	[1]
Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(18)	[2]	(5)	[2]
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	17		1
Derivative Liability	(1)	[1]	(4)	[1]
Gains (Losses) in Revenue [Member] | Weather Hedge Swaps [Member]
Derivative, Gain (Loss) on Derivative, Net	(10)		(16)		8
Gains (Losses) in Revenue [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	35		11		43
Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	11	[3],[4]	10	[3],[4]	(63)	[3],[4]
Not Designated as Hedging Instrument [Member] | Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	101	[5],[6],[7]	28	[10],[8],[9]
Derivative Liability, Fair Value, Gross Liability	1	[5],[6],[7]	4	[10],[8],[9]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	32	[5],[6],[7]	10	[8],[9]
Derivative Liability, Fair Value, Gross Liability	0	[5],[6],[7]	0	[8],[9]
Not Designated as Hedging Instrument [Member] | Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	14	[5],[6],[7]	4	[8],[9]
Derivative Liability, Fair Value, Gross Liability	83	[5],[6],[7]	21	[8],[9]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	2	[5],[6],[7]	1	[8],[9]
Derivative Liability, Fair Value, Gross Liability	18	[5],[6],[7]	5	[8],[9]
Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume	60,000		46,000
Swap [Member] | Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume	127,000		99,000
Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	127	[11]	21	[11]
Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value	0		9
Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value	4		4
Enable Midstream Partners [Member] | Forward Contracts [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset			1
2014To2015 [Member]
Weather Hedge, Bilateral Cap Amount	16
2013To2014 [Member]
Weather Hedge, Bilateral Cap Amount	16
2012To2013 [Member]
Weather Hedge, Bilateral Cap Amount	15
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	2		(2)
Enable Midstream Partners [Member] | Forward Contracts [Member] | Not Designated as Hedging Instrument [Member] | Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset			1
External Credit Rating, Investment Grade [Member]
Credit Risk Derivative Assets, at Fair Value	4	[12]	3	[12]
External Credit Rating, Investment Grade [Member] | Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	2	[11],[12]	1	[11],[12]
External Credit Rating, Investment Grade [Member] | Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value	0	[12]	1	[12]
External Credit Rating, Investment Grade [Member] | Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value	2	[12]	1	[12]
Natural Gas Distribution [Member] | Price Stabilization Activities [Member] | Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 0		$ 0		$ (38)

[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 $2 million and $(2) million during the years ended December 31, 2014 and 2013, respectively, related to physical forwards purchased from Enable.

[4] The Gains (Losses) in Expense: Natural Gas includes $-0-, $-0- and $(38) million of costs in 2014, 2013 and 2012, respectively, associated with price stabilization activities of the Natural Gas Distribution business segment that will be ultimately recovered through purchased gas adjustments.

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

[6] 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.

[7] Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable.

[8] 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 $13 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 less than $1 million.

[9] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 607 Bcf or a net 46 Bcf long position. Of the net long position, basis swaps constitute 99 Bcf.

[10] The $28 million Derivative Current Asset includes $1 million related to physical forwards purchased from Enable.

[11] 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.

[12] “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.