Condensed Consolidated Balance Sheets (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 334,912
Accounts receivable (less accumulated provision for doubtful accounts at September 30, 2011 and December 31, 2010: $14,913 and $18,335)	124,542	156,709
Unbilled revenues	8,158	38,361
Inventory	138,012	137,853
Derivative instruments, at fair value	313,537	225,339
Assets held for sale		207,678
Prepaid expenses and other	49,732	62,000
Total current assets	968,893	827,940
Equity in nonconsolidated investments	136,148	191,265
Property, plant and equipment	8,393,467	7,689,025
Less: accumulated depreciation and depletion	1,907,848	1,778,934
Net property, plant and equipment	6,485,619	5,910,091
Investments, available-for-sale		28,968
Regulatory assets	98,388	100,949
Other assets	31,146	39,225
Total assets	7,720,194	7,098,438
Current liabilities:
Current portion of long-term debt	25,315	6,000
Short-term loans		53,650
Accounts payable	252,030	212,134
Derivative instruments, at fair value	108,926	106,721
Other current liabilities	206,369	218,479
Total current liabilities	592,640	596,984
Long-term debt	1,978,596	1,943,200
Deferred income taxes and investment tax credits	1,502,625	1,274,888
Unrecognized tax benefits	36,991	41,451
Pension and other post-retirement benefits	38,845	44,135
Other credits	132,760	119,084
Total liabilities	4,282,457	4,019,742
Common stockholders' equity:
Common stock, no par value, authorized 320,000 shares (shares issued September 30, 2011 and December 31, 2010: 175,685 and 175,684)	1,731,246	1,723,898
Treasury stock, at cost (shares at September 30, 2011 and December 31, 2010: 26,247 and 26,531)	(473,925)	(479,072)
Retained earnings	2,085,980	1,795,766
Accumulated other comprehensive income	94,436	38,104
Total common stockholders' equity	3,437,737	3,078,696
Total liabilities and stockholders' equity	$ 7,720,194	$ 7,098,438