Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended				1 Months Ended	12 Months Ended		1 Months Ended
	Jul. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Southeast Supply Header Llc [Member]	Jul. 31, 2012 Waskom Gas Processing Company [Member]	Dec. 31, 2010 Waskom Gas Processing Company [Member]	Jun. 30, 2012 Waskom Gas Processing Company [Member]	Jul. 31, 2012 Waskom [Member]	Jul. 31, 2012 Gathering and Related Assets [Member]
Summary of Accounting Policies [Line Items]
Minimum Ownership Interest Percentage For Investments Recorded Using Entity Method		20.00%
Maximum Ownership Interest Percentage For Investments Recorded Using Entity Method		50.00%
Percentage of ownership interest					50.00%			50.00%
Length of Southeast Supply Header's interstate natural gas pipeline (in miles)		274
Investment during the period in Waskom							$ 20
Percentage of Ownership in Affiliate 2 Acquired						50.00%
Business Acquisition, Purchase Price Allocation, Remaining Interest	201
Business Acquisition, Cost of Acquired Entity, Cash Paid	273
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	253
Business Acquisition, Purchase Price Allocation, Goodwill Amount	16
Step acquisition gain	136	136	0	0
Acquisition	24	24							17	7
Allowance for doubtful accounts		23	24
Provision for doubtful accounts		15	25	30
Amount of removal costs recognized as a component of depreciation expense recorded as a regulatory liability		573	573
Amount of capitalized interest and allowance for funds used during construction		(2)	(1)	(7)
Write-downs of natural gas inventory to lower of cost or market		4	11
Materials and supplies		83	86
Natural gas		145	187
Total inventory		228	273
Margin deposits		12	17
Under Recovered Gas Costs		86	63
Over Recovered Gas Costs		$ 6	$ 14