Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Statement [Line Items]
Cash collateral posted with counterparties	$ 6				$ 6				$ 9
Corporate equities	2				2				1
Investments, including money market funds	11				11				11
Derivative Assets Fair Value	44				44				49
Natural gas derivatives	36				36				42
Total assets	49				49				54
Natural gas derivatives	7	[1]			7	[1]			16
Derivative Liability, Fair Value, Gross Liability	21				21				32
Total liabilities	7				7				16
Derivative Instruments, Liabilities, Physical Forwards Purchased	2				2
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance	4		3		2		6
Total gains (1)	2	[2]	0	[2]	5	[2]	4	[2]
Total settlements (1)	(1)	[2]	(2)	[2]	(2)	[2]	(8)	[2]
Transfers out of Level 3	0		0		0		(1)
Ending balance (2)	5	[3]	1	[3]	5	[3]	1	[3]
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date	2		(1)		4		0
Carrying Amount [Member]
Statement [Line Items]
Notes receivable - affiliated companies	363				363				0
Long-term debt	2,120				2,120				2,641
Fair Value [Member]
Statement [Line Items]
Notes receivable - affiliated companies	362				362				0
Long-term debt	2,386				2,386				3,094
Fair Value, Inputs, Level 1 [Member]
Statement [Line Items]
Corporate equities	2				2				1
Investments, including money market funds	11				11				11
Derivative Assets Fair Value	4				4				1
Total assets	17				17				13
Derivative Liability, Fair Value, Gross Liability	4	[1]			4	[1]			5
Total liabilities	4				4				5
Fair Value, Inputs, Level 2 [Member]
Statement [Line Items]
Corporate equities	0				0				0
Investments, including money market funds	0				0				0
Derivative Assets Fair Value	33				33				40
Total assets	33				33				40
Derivative Liability, Fair Value, Gross Liability	15	[1]			15	[1]			21
Total liabilities	15				15				21
Fair Value, Inputs, Level 3 [Member]
Statement [Line Items]
Corporate equities	0				0				0
Investments, including money market funds	0				0				0
Derivative Assets Fair Value	7				7				7
Total assets	7				7				7
Derivative Liability, Fair Value, Gross Liability	2	[1]			2	[1]			5
Total liabilities	2				2				5
Netting [Member]
Statement [Line Items]
Corporate equities	0	[4]			0	[4]			0	[5]
Investments, including money market funds	0	[4]			0	[4]			0	[5]
Derivative Asset, Fair Value, Gross Liability	(8)	[4]			(8)	[4]			(6)	[5]
Derivative Liability, Fair Value, Gross Asset	$ (14)	[1],[4]			$ (14)	[1],[4]			$ (15)	[5]
Minimum [Member] | Fair Value, Inputs, Level 3 [Member]
Statement [Line Items]
Option volatilities low range	0.00%				0.00%
Maximum [Member] | Fair Value, Inputs, Level 3 [Member]
Statement [Line Items]
Option volatilities low range	52.00%				52.00%
Forward Contracts [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member]
Statement [Line Items]
Illiquid forward price low range					2.85
Forward Contracts [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member]
Statement [Line Items]
Illiquid forward price low range					4.48

[1] The (Level 2) Natural gas derivative liability of $15 million includes $2 million related to physical forwards purchased from Enable.

[2] CERC did not have Level 3 unrealized gains (losses) or settlements related to price stabilization activities of the Natural Gas Distribution business segment during either the three or nine months ended September 30, 2012 or 2013.

[3] CERC did not have significant Level 3 purchases, sales or transfers into Level 3 during either the three or nine months ended September 30, 2012 or 2013.

[4] Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $6 million posted with the same counterparties.

[5] Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $9 million posted with the same counterparties.