Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 154,856	$ 124,718
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	77,478	77,685
Allowance for equity funds used during construction (equity AFUDC)	(18,366)	(8,135)
Changes in operating assets and liabilities:
Receivables - affiliates	(452)	449
Receivables - trade and other	6,231	15,720
Transportation and exchange gas receivable	(1,467)	722
Inventories	(14,370)	(7,360)
Payables - affiliates	(1,064)	(5,407)
Payables - trade	(11,738)	(4,185)
Accrued liabilities	(71,928)	4,791
Asset retirement obligations - non-current	24,670	15,331
Asset retirement obligations - removal costs	(222)	(990)
Other, net	6,945	10,012
Net cash provided by operating activities	150,573	223,351
Cash flows from financing activities:
Proceeds from long-term debt	0	998,250
Payments for debt issuance costs	(13)	(8,235)
Cash distributions to parent	(100,000)	(175,000)
Cash contributions from parent	110,000	112,000
Net cash provided by financing activities	9,987	927,015
Cash flows from investing activities:
Property, plant and equipment additions, net of equity AFUDC	(374,220)	(230,968)
Contributions and advances for construction costs	131,874	57,196
Disposal of property, plant and equipment, net	(2,131)	(349)
Advances to affiliate, net	91,733	(964,646)
Return of capital from unconsolidated affiliates	1,225	883
Purchase of ARO Trust investments	(22,418)	(33,321)
Proceeds from sale of ARO Trust investments	10,177	18,718
Proceeds from insurance	3,200	2,121
Net cash used in investing activities	(160,560)	(1,150,366)
Increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	0	0
Increase to property, plant and equipment, net of equity AFUDC	(434,824)	(264,841)
Changes in related accounts payable and accrued liabilities	60,604	33,873
Property, plant and equipment additions, net of equity AFUDC	$ (374,220)	$ (230,968)