Consolidated Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net Income	$ 272,466	$ 279,658	$ 270,776
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	266,981	260,069	252,131
Allowance for equity funds used during construction (Equity AFUDC)	(13,222)	(10,588)	(8,539)
Changes in operating assets and liabilities:
Receivables - affiliates	3,247	(982)	1,702
Receivables - others	(4,186)	(11,155)	6,714
Transportation and exchange gas receivable	2,038	(2,497)	4,833
Inventories	673	50,295	(46,261)
Payables - affiliates	15,069	(1,832)	(23,485)
Payables - others	3,727	14,577	15,888
Accrued liabilities	8,256	27,775	617
Asset retirement obligation removal costs	(41,052)	(43,666)	(6,990)
Reserve for rate refunds	0	0	(564)
Other, net	27,452	9,990	42,661
Net cash provided by operating activities	541,449	571,644	509,483
Cash flows from financing activities:
Additions to long-term debt	398,804	372,518	0
Retirement of long-term debt	(325,000)	(300,000)	0
Debt issue costs	(4,403)	(3,846)	0
Cash distributions	(246,259)	(219,000)	(333,791)
Cash contributions from parent	150,000	115,000	75,000
Other	(3,333)	(4,681)	1,146
Net cash used in financing activities	(30,191)	(40,009)	(257,645)
Cash flows from investing activities:
Property, plant and equipment additions, net of equity AFUDC*	(475,450)	(385,671)	(376,502)
Disposal of property, plant and equipment, net	7,157	2,698	13,959
Advances to affiliates, net	(58,554)	(144,773)	126,999
Return of capital from unconsolidated affiliates	11,327	1,925	0
Contributions to unconsolidated affiliates	(5,806)	(14,834)	0
Purchase of ARO Trust investments	(34,430)	(41,310)	(46,952)
Proceeds from sale of ARO Trust investments	43,205	56,576	31,001
Other, net	1,314	(6,230)	(303)
Net cash used in investing activities	(511,237)	(531,619)	(251,798)
Increase in cash	21	16	40
Cash at beginning of period	164	148	108
Cash at end of period	$ 185	$ 164	$ 148