Condensed Consolidated Balance Sheet (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current Assets:
Cash	$ 139	$ 185
Receivables:
Affiliates	2,924	2,656
Advances to affiliate	385,343	312,165
Trade and other	131,891	125,775
Transportation and exchange gas receivables	4,748	2,876
Inventories	51,960	45,918
Regulatory assets	47,261	36,706
Other	7,323	14,342
Total current assets	631,589	540,623
Investments, at cost plus equity in undistributed earnings	54,767	55,603
Property, Plant and Equipment:
Natural gas transmission plant	8,573,438	8,506,189
Less-Accumulated depreciation and amortization	2,974,574	2,954,276
Total property, plant and equipment, net	5,598,864	5,551,913
Other Assets:
Regulatory assets	206,690	214,912
Other	45,279	47,764
Total other assets	251,969	262,676
Total assets	6,537,189	6,410,815
Payables:
Affiliates	26,533	32,006
Trade and other	135,785	119,307
Transportation and exchange gas payables	2,948	3,513
Accrued liabilities	171,248	139,333
Total current liabilities	336,514	294,159
Long-Term Debt	1,428,356	1,428,323
Other Long-Term Liabilities:
Asset retirement obligations	253,766	253,398
Regulatory liabilities	237,718	232,888
Other	5,049	5,339
Total other long-term liabilities	496,533	491,625
Contingent Liabilities and Commitments (Note 2)
Owner's Equity:
Member's capital	2,048,412	1,993,412
Retained earnings	2,227,994	2,204,018
Accumulated other comprehensive loss	(620)	(722)
Total owner's equity	4,275,786	4,196,708
Total liabilities and owner's equity	$ 6,537,189	$ 6,410,815