Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues [Abstract]
Natural gas sales	$ 127,821	$ 99,100	$ 86,720
Natural gas transportation	1,784,794	1,531,778	1,397,341
Natural gas storage	136,666	137,348	122,555
Other	10,600	6,779	9,519
Total operating revenues	2,059,881	1,775,005	1,616,135
Operating Costs and Expenses:
Cost of natural gas sales	127,821	99,100	86,720
Cost of natural gas transportation	38,749	19,589	19,689
Operation and maintenance	399,293	401,871	316,989
Administrative and general	189,588	182,121	168,759
Depreciation and amortization	366,566	318,058	307,707
Taxes - other than income taxes	67,537	65,612	60,119
Regulatory charge (credit) resulting from Tax Reform (Note 1)	(20,867)	471,096	0
Other expense, net	64,918	63,644	57,064
Total operating costs and expenses	1,233,605	1,621,091	1,017,047
Operating Income	826,276	153,914	599,088
Other (Income) and Other Expenses:
Interest expense - affiliate	60	60	60
Interest expense - other	218,126	158,814	151,234
Interest income - affiliate	(7,606)	(3,507)	(2,201)
Interest income - other	(3,448)	(2,782)	(2,185)
Allowance for equity and borrowed funds used during construction (AFUDC)	(116,347)	(92,013)	(68,964)
Equity in (earnings) loss of unconsolidated affiliates	(1,068)	6,188	(5,914)
Miscellaneous other (income) expenses, net	(4,520)	31,426	3,683
Total other (income) and other expenses	85,197	98,186	75,713
Net Income	741,079	55,728	523,375
Other comprehensive income:
Equity interest in unrealized gain on interest rate hedges (includes $(143), $103, and $167 for the years ended December 31, 2018, 2017, and 2016, respectively, of accumulated other comprehensive income reclassification for equity interest in realized losses (gains) on interest rate hedges)	197	327	41
Comprehensive Income	$ 741,276	$ 56,055	$ 523,416