Derivative Instruments Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014 MMcf
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments, Assets, Physical Forwards Purchased	$ 128				$ 149
Derivative Liability, Fair Value, Gross Liability	82				102
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(1)		9
Derivative, Fair Value, Net [Abstract]
Total fair value of the derivative instruments that contain credit risk contingency features that are in a net liability position	3				2
Collateral Already Posted, Aggregate Fair Value	1				1
Credit Risk Contingent Feature assets	3				2
Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative, Nonmonetary Notional Amount, Volume	749,000				804,000
Gross Amounts Recognized (1)	46	[1]			47	[1]
Derivative, Fair Value, Offsets, Net	60				64
Derivative Assets (Liabilities), at Fair Value, Net	106	[2]			111	[2]
collateral Netting	60				64
Energy Related Derivative [Member] | Current Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	91	[1]			115	[1]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(9)				(16)
Derivative Asset	82	[2]			99	[2]
Energy Related Derivative [Member] | Other Noncurrent Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	37	[1]			34	[1]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(2)				(2)
Derivative Asset	35	[2]			32	[2]
Energy Related Derivative [Member] | Current Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(63)	[1]			(84)	[1]
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	54				65
Derivative Liability	(9)	[2]			(19)	[2]
Energy Related Derivative [Member] | Other Noncurrent Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	(19)	[1]			(18)	[1]
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	17				17
Derivative Liability	(2)	[2]			(1)	[2]
Energy Related Derivative [Member] | Gains (Losses) in Revenue
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(133)		(101)
Energy Related Derivative [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	132	[3]	110	[3]
Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Current Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments, Assets, Physical Forwards Purchased	82	[4],[5]			101	[6],[7]
Derivative Liability, Fair Value, Gross Liability	0	[4],[5]			1	[6],[7]
Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Noncurrent Assets [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments, Assets, Physical Forwards Purchased	35	[4],[5]			32	[6],[7]
Derivative Liability, Fair Value, Gross Liability	0	[4],[5]			0	[6],[7]
Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Current Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments, Assets, Physical Forwards Purchased	9	[4],[5]			14	[6],[7]
Derivative Liability, Fair Value, Gross Liability	63	[4],[5]			83	[6],[7]
Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Noncurrent Liabilities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative Instruments, Assets, Physical Forwards Purchased	2	[4],[5]			2	[6],[7]
Derivative Liability, Fair Value, Gross Liability	19	[4],[5]			18	[6],[7]
Long [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative, Nonmonetary Notional Amount, Volume	126,000				60,000
Swap [Member] | Long [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [Abstract]
Derivative, Nonmonetary Notional Amount, Volume	125,000				127,000
Enable Midstream Partners [Member] | Forward Contracts [Member] | Energy Related Derivative [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	$ 0		$ 2

[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 Condensed 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 months ended March 31, 2015 and 2014, respectively, related to physical forwards purchased from Enable.

[4] The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 749 billion cubic feet (Bcf) or a net 126 Bcf long position. Of the net long position, basis swaps constitute 125 Bcf.

[5] 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 $106 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 $60 million.

[6] 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.

[7] 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 $111 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 $64 million.