Supplemental Financial Information (Unaudited) (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended											12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Operating revenues	$ 1,065,749,000		$ 1,152,181,000	$ 930,757,000	$ 901,805,000	$ 1,042,551,000		$ 1,125,923,000		$ 906,444,000	$ 834,777,000	$ 4,050,492,000		$ 3,909,695,000		$ 4,176,501,000
Operating expenses	939,172,000		1,032,760,000	848,454,000	823,739,000	912,377,000		1,016,961,000	[1]	817,782,000	751,848,000	3,644,125,000		3,498,968,000		4,329,598,000
Operating income (loss)	126,577,000		119,421,000	82,303,000	78,066,000	130,174,000		108,962,000	[1]	88,662,000	82,929,000	406,367,000		410,727,000		(153,097,000)
Income (loss) from continuing operations	74,088,000		64,100,000	45,235,000	42,529,000	92,300,000	[2]	61,010,000	[1]	48,938,000	41,772,000	225,952,000		244,020,000		(123,274,000)
Income (loss) from discontinued operations, net of tax	(13,080,000)	[3]	(126,000)	(168,000)	448,000	(3,361,000)		0		0	0	(12,926,000)	[4]	(3,361,000)	[4]	0	[4]
Net income (loss)	61,008,000	[3]	63,974,000	45,067,000	42,977,000	88,939,000	[2]	61,010,000	[1]	48,938,000	41,772,000	213,026,000		240,659,000		(123,274,000)
Earnings per common share - basic [Abstract]
Earnings (Loss) Before Discontinued Operations	$ 0.39		$ 0.34	$ 0.24	$ 0.22	$ 0.49	[2]	$ 0.32	[1]	$ 0.26	$ 0.22	$ 1.19		$ 1.29		$ (0.67)
Discontinued Operations, Net of Tax	$ (0.07)	[3]	$ 0	$ 0	$ 0.01	$ (0.02)		$ 0		$ 0	$ 0	$ (0.07)		$ (0.01)		$ 0.00
Earnings (Loss) Per Common Share - Basic	$ 0.32	[3]	$ 0.34	$ 0.24	$ 0.23	$ 0.47	[2]	$ 0.32	[1]	$ 0.26	$ 0.22	$ 1.12		$ 1.28		$ (0.67)
Earnings per common share - diluted [Abstract]
Earnings (Loss) Before Discontinued Operations	$ 0.39		$ 0.34	$ 0.24	$ 0.22	$ 0.49	[2]	$ 0.32	[1]	$ 0.26	$ 0.22	$ 1.19		$ 1.29		$ (0.67)
Discontinued Operations, Net of Tax	$ (0.07)	[3]	$ 0	$ 0	$ 0.01	$ (0.02)		$ 0		$ 0	$ 0	$ (0.07)		$ (0.02)		$ 0.00
Earnings (Loss) Per Common Share - Diluted	$ 0.32	[3]	$ 0.34	$ 0.24	$ 0.23	$ 0.47	[2]	$ 0.32	[1]	$ 0.26	$ 0.22	$ 1.12		$ 1.27		$ (0.67)
Weighted average common shares outstanding - basic	188,794		188,794	188,794	188,671	188,281		188,170		188,129	187,963	188,763		188,137		185,175	[5]
Weighted Average Common Shares Outstanding - Diluted	188,932		188,797	188,968	188,815	188,374		188,338		188,267	188,220	188,905		188,229		185,175	[5]
Natural gas gathering arbitration charge, after tax								16,500,000						16,500,000
Arbitration charge after tax	13,000,000											13,000,000
Recognized gain on sale of ownership interests, after tax						$ 13,800,000

[1] 2010 reflects a natural gas gathering arbitration charge of $16.5 million (after tax). For more information, see Note 19.

[2] 2010 reflects a $13.8 million (after tax) gain on the sale of the Brazilian Transmission Lines. For more information, see Note 4.

[3] 2011 reflects an arbitration charge of $13.0 million (after tax) related to a guarantee of a construction contract. For more information, see Note 19.

[4] Reflected in the Other category.

[5] Due to the loss on common stock, 825 outstanding stock options, 18 restricted stock grants and 656 performance share awards were excluded from the computation of diluted loss per common share as their effect was antidilutive.