Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 1,066,168	$ 880,036	$ 963,296
Adjustments to reconcile net cash provided (used) by operating activities:
Depreciation and amortization	489,524	463,757	433,480
Impairment of assets	2,336	170,128	0
Allowance for equity funds used during construction (equity AFUDC)	(17,080)	(14,889)	(28,785)
Regulatory credit resulting from tax rate changes	(30,752)	(30,752)	(24,202)
Equity in earnings of unconsolidated affiliates	0	0	(3,216)
Distributions from unconsolidated affiliates	0	0	4,908
Changes in operating assets and liabilities:
Receivables - affiliates	(5,967)	(342)	582
Receivables - trade and other	(15,355)	14,742	(52,307)
Transportation and exchange gas receivable	(3,058)	1,733	(1,845)
Regulatory assets - current	(51,490)	6,579	26,330
Regulatory assets - non-current	30,501	11,361	3,622
Inventories	1,860	8,695	(1,787)
Payables - affiliates	36,452	(15,064)	(2,981)
Payables - trade	953	(915)	(18,842)
Accrued liabilities	(4,302)	22,881	(1,723)
Asset retirement obligations	7,177	12,027	15,713
Reserve for rate refunds	0	(188,842)	188,842
Deferred revenue	(10,566)	(10,568)	(10,566)
Other, net	(47,745)	(36,990)	(36,365)
Net cash provided by operating activities	1,448,656	1,293,577	1,454,154
FINANCING ACTIVITIES:
Proceeds from long-term debt	0	1,195,629	0
Proceeds from other financing obligations	3,297	8,725	41,513
Payments on other financing obligations	(22,635)	(20,366)	(17,436)
Payments for debt issuance costs	(59)	(11,441)	0
Cash distributions to parent	(343,731)	(1,020,000)	(824,000)
Cash contributions from parent	417,000	115,000	0
Advances from affiliate, net	0	(252,549)	252,549
Net cash provided by (used in) financing activities	53,872	14,998	(547,374)
INVESTING ACTIVITIES:
Capital expenditures	(481,280)	(649,459)	(901,374)
Contributions and advances for construction costs	36,945	35,284	47,034
Disposal of property, plant and equipment, net	(32,565)	(43,900)	(45,720)
Advances to affiliate, net	(1,026,634)	(642,734)	33,034
Contributions to unconsolidated affiliates	0	0	12,250
Purchase of ARO Trust investments	(28,804)	(53,357)	(72,946)
Proceeds from sale of ARO Trust investments	29,810	45,591	45,479
Other, net	0	0	37
Net cash used in investing activities	(1,502,528)	(1,308,575)	(906,780)
Cash and Cash Equivalents, Period Increase (Decrease) [Abstract]
Increase (decrease) in cash	0	0	0
Cash at beginning of period	0	0	0
Cash at end of period	0	0	0
Increase to property, plant and equipment, exclusive of equity AFUDC	(512,293)	(582,896)	(854,761)
Changes in related accounts payable and accrued liabilities	31,013	(66,563)	(46,613)
Capital expenditures	(481,280)	(649,459)	(901,374)
Supplemental disclosures of cash flow information:
Interest (exclusive of amount capitalized)	313,828	299,470	268,559
Income taxes	$ 127	$ 352	$ 76