Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 MMcf		Dec. 31, 2011 MMcf		Dec. 31, 2010
Derivative Assets Investment Grade Non Trading	$ 1	[1]	$ 1	[1]
Derivative Assets Non Trading	42		107
Increased (Decreased) Natural Gas Revenues From Unrealized Net Gains (Losses)	(68)		38		18
Increased (Decreased) Natural Gas Expense From Unrealized Net Losses (Gains)	(52)		30		14
Net Unrealized Gain (Loss)	(16)		8		4
Weather Hedges Gain Loss Recognized	8		(1)		0
Derivative gross volumes on natural gas contracts (in MMcf)	489,000		633,000
Net long position (in MMcf)	101,000		84,000
Amount of net long position constituted by basis swaps (in MMcf)	73,000		74,000
Amount of net long position comprised of price stabilization activities of the Natural Gas Distribution business segment (MMcf)			6,000
Total non-trading derivative assets and liabilities net of collateral	26		55
Collateral Netting	9		56
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(20)		(42)
Total fair value of derivative instruments that contain credit risk contingent features that are in a net liability position	5		39
Aggregate fair value of assets already posted as collateral	1		1
Credit risk contingent feature assets	5		38
Weather Hedge Maximum Payment Limit	11
Gains (Losses) in Revenue [Member] | Natural gas derivatives [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	43		102
Gains (Losses) in Expense: Natural Gas [Member] | Natural gas derivatives [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(63)	[2]	(144)	[2]
Costs associated with price stabilization activities of the Natural Gas Distribution business segment included in Expenses	(38)		(107)
Energy Marketers [Member]
Derivative Assets Investment Grade Non Trading	1	[1]	1	[1]
Derivative Assets Non Trading	1		7
Financial Institutions [Member]
Derivative Assets Investment Grade Non Trading	0	[1]	0	[1]
Derivative Assets Non Trading	0		0
Retail End Users [Member]
Derivative Assets Investment Grade Non Trading	0	[1],[3]	0	[1],[3]
Derivative Assets Non Trading	41	[3]	100	[3]
Not Designated as Hedging Instrument [Member]
Derivative Assets Fair Value	49	[4],[5]	123	[6],[7]
Derivative Liabilities Fair Value	32	[4],[5]	124	[6],[7]
Not Designated as Hedging Instrument [Member] | Current Assets [Member] | Natural gas derivatives [Member]
Derivative Assets Fair Value	37	[4],[5],[8]	88	[6],[7],[8]
Derivative Liabilities Fair Value	1	[4],[5],[8]	1	[6],[7],[8]
Not Designated as Hedging Instrument [Member] | Other Assets [Member] | Natural gas derivatives [Member]
Derivative Assets Fair Value	6	[4],[5],[8]	20	[6],[7],[8]
Derivative Liabilities Fair Value	0	[4],[5],[8]	0	[6],[7],[8]
Not Designated as Hedging Instrument [Member] | Current Liabilities [Member] | Natural gas derivatives [Member]
Derivative Assets Fair Value	5	[4],[5],[8]	15	[6],[7],[8]
Derivative Liabilities Fair Value	27	[4],[5],[8]	110	[6],[7],[8]
Not Designated as Hedging Instrument [Member] | Other Liabilities [Member] | Natural gas derivatives [Member]
Derivative Assets Fair Value	1	[4],[5],[8]	0	[6],[7],[8]
Derivative Liabilities Fair Value	$ 4	[4],[5],[8]	$ 13	[6],[7],[8]

[1] “Investment grade” is primarily determined using publicly available credit ratings and considering credit support (such as parent company guaranties) and collateral, which encompass cash and standby letters of credit. For unrated counterparties, CERC determines a synthetic credit rating by performing financial statement analysis and considering contractual rights and restrictions and collateral.

[2] The Gains (Losses) in Expense: Natural Gas includes $(107) million and $(38) million of costs in 2011 and 2012, respectively, associated with price stabilization activities of the Natural Gas Distribution business segment that will be ultimately recovered through purchased gas adjustments.

[3] Retail end users represent customers who have contracted to fix the price of a portion of their physical gas requirements for future periods.

[4] The net of total non-trading derivative assets and liabilities is a $26 million asset as shown on CERC’s Consolidated Balance Sheets, and is comprised of the natural gas contracts derivative assets and liabilities separately shown above offset by collateral netting of $9 million.

[5] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 489 Bcf or a net 101 Bcf long position. Of the net long position, basis swaps constitute 73 Bcf.

[6] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 633 billion cubic feet (Bcf) or a net 84 Bcf long position. Of the net long position, basis swaps constitute 74 Bcf and volumes associated with price stabilization activities of the Natural Gas Distribution business segment constitute 6 Bcf.

[7] The net of total non-trading derivative assets and liabilities is a $55 million asset as shown on CERC’s Consolidated Balance Sheets, and is comprised of the natural gas contracts derivative assets and liabilities separately shown above offset by collateral netting of $56 million.

[8] Natural gas contracts are subject to master netting arrangements and are presented on a net basis in the Consolidated Balance Sheets. This netting causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets.