Derivative Instruments Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2014 MMcf Years		Mar. 31, 2013		Dec. 31, 2013 MMcf
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	$ 41				$ 43
Derivative Liabilities Fair Value	(26)				(30)
Derivative, fair value, offsets, net					1
Net Amount Presented in the Consolidated Balance Sheets (2)	14				13
Cash Collateral Posted with Same Counterparties	(1)
Derivative gross volumes on natural gas contracts (MMcf)	547,000				607,000
Net long position (MMcf)	92,000				46,000
Amount of net long position constituted by basis swaps (MMcf)	91,000				99,000
Total fair value of the derivative instruments that contain credit risk contingency features that are in a net liability position	1				1
Collateral Already Posted, Aggregate Fair Value	1				1
Credit Risk Contingent Feature assets	1				1
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Term of normal weather used as the basis for weather hedges (in years)	10
Gains (Losses) Recognized Related to Weather Hedges	(7)		(3)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	9		2
Derivative Instruments, Assets, Physical Forwards Purchased					1
Natural Gas Derivatives [Member]
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized (1)	15	[1]			13	[1]
Derivative, fair value, offsets, net					0
Net Amount Presented in the Consolidated Balance Sheets (2)	14	[2]			13	[2]
Cash Collateral Posted with Same Counterparties	(1)
Natural Gas Derivatives [Member] | Current Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	30	[1]			32	[1]
Derivative Asset, Fair Value, Gross Liability	(6)				(8)
Net Amount Presented in the Consolidated Balance Sheets (2)	24	[2]			24	[2]
Natural Gas Derivatives [Member] | Other Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	11	[1]			11	[1]
Derivative Asset, Fair Value, Gross Liability	(2)				(1)
Net Amount Presented in the Consolidated Balance Sheets (2)	9	[2]			10	[2]
Natural Gas Derivatives [Member] | Current Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Liabilities Fair Value	(22)	[1]			(25)	[1]
Derivative Liability, Fair Value, Gross Asset	5				8
Net Amount Presented in the Consolidated Balance Sheets (2)	(17)	[2]			(17)	[2]
Natural Gas Derivatives [Member] | Other Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Liabilities Fair Value	(4)	[1]			(5)	[1]
Derivative Liability, Fair Value, Gross Asset	2				1
Net Amount Presented in the Consolidated Balance Sheets (2)	(2)	[2]			(4)	[2]
Natural Gas Derivatives [Member] | Gains (Losses) in Revenue [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(101)		(14)
Natural Gas Derivatives [Member] | Gains (Losses) in Expense: Natural Gas [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	110	[3]	16	[3]
Derivative Instruments Physical Forwards Purchased	2
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Current Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	29	[4],[5]			28	[6],[7],[8]
Derivative Liabilities Fair Value	(4)	[4],[5]			(4)	[6],[7],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Other Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	11	[4],[5]			10	[6],[8]
Derivative Liabilities Fair Value	(2)	[4],[5]			0	[6],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Current Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	1	[4],[5]			4	[6],[8]
Derivative Liabilities Fair Value	(18)	[4],[5]			(21)	[6],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Other Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Assets Fair Value	0	[4],[5]			1	[6],[8]
Derivative Liabilities Fair Value	(2)	[4],[5]			(5)	[6],[8]
2012 - 2013 [Member]
Derivatives, Fair Value [Line Items]
Weather Hedge, Amount, maximum	15
2013 - 2014 [Member]
Derivatives, Fair Value [Line Items]
Weather Hedge, Amount, maximum	$ 16

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

[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] The Gains (Losses) in Expense: Natural Gas includes $2 million during the three months ended March 31, 2014 related to physical forwards purchased from Enable.

[4] Natural gas contracts are presented on a net basis in the Condensed 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 Condensed Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $14 million asset as shown on CERC’s Condensed 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 $(1) million.

[5] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 547 Bcf or a net 92 Bcf long position. Of the net long position, basis swaps constitute 91 Bcf.

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

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

[8] Natural gas contracts are presented on a net basis in the Condensed 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 Condensed Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $13 million asset as shown on CERC’s Condensed 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.