Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Revenues:
Natural gas sales	$ 86,720	$ 125,774	$ 121,397
Natural gas transportation	1,397,341	1,318,656	1,166,244
Natural gas storage	122,555	137,983	140,344
Other	9,519	10,106	5,152
Total operating revenues	1,616,135	1,592,519	1,433,137
Operating Costs and Expenses:
Cost of natural gas sales	86,720	125,774	121,397
Cost of natural gas transportation	19,689	26,501	31,629
Operation and maintenance	316,989	288,386	271,603
Administrative and general	168,759	179,489	183,760
Depreciation and amortization	307,707	277,850	270,181
Taxes - other than income taxes	60,119	49,567	44,521
Other expense, net	57,064	57,800	37,208
Total operating costs and expenses	1,017,047	1,005,367	960,299
Operating Income	599,088	587,152	472,838
Other (Income) and Other Expenses:
Interest expense - affiliate	60	64	70
Interest expense - other	151,234	82,774	84,917
Interest income - affiliate	(2,201)	(28)	(49)
Interest income - other	(2,185)	(1,933)	(1,782)
Allowance for equity and borrowed funds used during construction (AFUDC)	(68,964)	(63,072)	(25,046)
Equity in earnings of unconsolidated affiliates	(5,914)	(5,593)	(5,783)
Miscellaneous other (income) expenses, net	3,683	(517)	(2,373)
Total other (income) and other expenses	75,713	11,695	49,954
Net Income	523,375	575,457	422,884
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes $167, $316, and $344 for the years ended December 31, 2016, 2015, and 2014, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses on interest rate hedges)	41	84	143
Comprehensive Income	$ 523,416	$ 575,541	$ 423,027