Derivative Instruments Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014 MMcf Years		Jun. 30, 2013		Dec. 31, 2013 MMcf
Derivatives, Fair Value [Line Items]
Term of normal weather used as the basis for weather hedges (in years)					10
Gains (Losses) Recognized Related to Weather Hedges	$ 0		$ (3)		$ (7)		$ (6)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	46				46				43
Derivative Liability, Fair Value, Gross Liability	22				22				30
Derivative gross volumes on natural gas contracts (MMcf)					603,000				607,000
Net long position (MMcf)					97,000				46,000
Amount of net long position constituted by basis swaps (MMcf)					97,000				99,000
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	9		9		18		11
Derivative Instruments, Assets, Physical Forwards Purchased									1
Derivative, Fair Value, Net [Abstract]
Derivative, fair value, offsets, net									1
Net Amount Presented in the Consolidated Balance Sheets (2)	24				24				13
Total fair value of the derivative instruments that contain credit risk contingency features that are in a net liability position	1				1				1
Collateral Already Posted, Aggregate Fair Value	1				1				1
Credit Risk Contingent Feature assets	1				1				1
Natural Gas Derivatives [Member]
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized (1)	24	[1]			24	[1]			13	[1]
Derivative, fair value, offsets, net	0				0				0
Net Amount Presented in the Consolidated Balance Sheets (2)	24	[2]			24	[2]			13	[2]
Natural Gas Derivatives [Member] | Current Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Amount Offset Against Collateral	32	[1]			32	[1]			32	[1]
Derivative Asset, Fair Value, Gross Liability	(6)				(6)				(8)
Net Amount Presented in the Consolidated Balance Sheets (2)	26	[2]			26	[2]			24	[2]
Natural Gas Derivatives [Member] | Other Assets [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Asset, Fair Value, Amount Offset Against Collateral	14	[1]			14	[1]			11	[1]
Derivative Asset, Fair Value, Gross Liability	(2)				(2)				(1)
Net Amount Presented in the Consolidated Balance Sheets (2)	12	[2]			12	[2]			10	[2]
Natural Gas Derivatives [Member] | Current Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Amount Offset Against Collateral	(18)	[1]			(18)	[1]			(25)	[1]
Derivative Liability, Fair Value, Gross Asset	6				6				8
Net Amount Presented in the Consolidated Balance Sheets (2)	(12)	[2]			(12)	[2]			(17)	[2]
Natural Gas Derivatives [Member] | Other Liabilities [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Amount Offset Against Collateral	(4)	[1]			(4)	[1]			(5)	[1]
Derivative Liability, Fair Value, Gross Asset	2				2				1
Net Amount Presented in the Consolidated Balance Sheets (2)	(2)	[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	5		27		(96)		13
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	4	[3]	(18)	[3]	114	[3]	(2)	[3]
Derivative Instruments Physical Forwards Purchased	0				2
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Current Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	31	[4],[5]			31	[4],[5]			28	[6],[7],[8]
Derivative Liability, Fair Value, Gross Liability	5	[4],[5]			5	[4],[5]			4	[6],[7],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Other Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	14	[4],[5]			14	[4],[5]			10	[6],[8]
Derivative Liability, Fair Value, Gross Liability	2	[4],[5]			2	[4],[5]			0	[6],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Current Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	1	[4],[5]			1	[4],[5]			4	[6],[8]
Derivative Liability, Fair Value, Gross Liability	13	[4],[5]			13	[4],[5]			21	[6],[8]
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member] | Other Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset	0	[4],[5]			0	[4],[5]			1	[6],[8]
Derivative Liability, Fair Value, Gross Liability	2	[4],[5]			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 $-0- and $2 million during the three and six months ended June 30, 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 $24 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.

[5] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 603 Bcf or a net 97 Bcf long position. Of the net long position, basis swaps constitute 97 Bcf.

[6] 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.

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

[8] 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.