Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Revenues:
Natural gas sales	$ 65,120	$ 108,359	$ 99,346
Natural gas transportation	1,022,990	983,554	930,704
Natural gas storage	140,390	142,556	146,820
Other	5,601	8,045	5,125
Total operating revenues	1,234,101	1,242,514	1,181,995
Operating Costs and Expenses:
Cost of natural gas sales	65,120	108,359	99,346
Cost of natural gas transportation	31,815	35,674	32,231
Operation and maintenance	292,610	274,735	249,060
Administrative and general	174,610	148,113	148,589
Depreciation and amortization	266,445	259,660	252,049
Taxes - other than income taxes	52,210	48,434	46,064
Other expense, net	21,230	12,988	15,189
Total operating costs and expenses	904,040	887,963	842,528
Operating Income	330,061	354,551	339,467
Other (Income) and Other Deductions:
Interest expense - affiliate	309	262	353
Interest expense - other	88,766	94,920	94,620
Interest income - affiliates	(35)	(29)	(2,231)
Interest income - other	(2,351)	(2,119)	(882)
Allowance for equity and borrowed funds used during construction (AFUDC)	(19,257)	(15,339)	(12,349)
Equity in earnings of unconsolidated affiliates	(7,458)	(5,164)	(5,805)
Miscellaneous other (income) deductions, net	(2,379)	2,362	(5,015)
Total other (income) and other deductions	57,595	74,893	68,691
Net Income	272,466	279,658	270,776
Equity interest in unrealized gain (loss) on interest rate hedge	(376)	(519)	891
Comprehensive Income	$ 272,090	$ 279,139	$ 271,667