CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 831,251	$ 0
Accounts receivable (less accumulated provision for doubtful accounts: $16,371 in 2011; $18,335 in 2010)	153,321	156,709
Unbilled revenues	30,257	38,361
Inventory	123,960	137,853
Derivative instruments, at fair value	512,161	225,339
Assets held for sale		207,678
Prepaid expenses and other	39,184	62,000
Total current assets	1,690,134	827,940
Equity in nonconsolidated investments	136,972	191,265
Property, plant and equipment	8,768,713	7,689,025
Less: accumulated depreciation and depletion	1,962,404	1,778,934
Net property, plant and equipment	6,806,309	5,910,091
Investments, available-for-sale		28,968
Regulatory assets	94,095	100,949
Other	45,209	39,225
Total assets	8,772,719	7,098,438
Current liabilities:
Current portion of long-term debt	219,315	6,000
Short-term loans		53,650
Accounts payable	256,757	212,134
Derivative instruments, at fair value	123,306	106,721
Other current liabilities	205,532	218,479
Total current liabilities	804,910	596,984
Long-term debt	2,527,627	1,943,200
Deferred income taxes and investment tax credits	1,618,944	1,274,888
Unrecognized tax benefits	13,611	41,451
Pension and other post-retirement benefits	47,589	44,135
Other credits	166,208	119,084
Total liabilities	5,178,889	4,019,742
Common stockholders' equity:
Common stock, no par value, authorized 320,000 shares: shares issued: 175,684 in 2011 and 2010	1,734,994	1,723,898
Treasury stock, shares at cost: 26,207 in 2011 and 26,531 in 2010	(473,215)	(479,072)
Retained earnings	2,143,910	1,795,766
Accumulated other comprehensive income	188,141	38,104
Total common stockholders' equity	3,593,830	3,078,696
Total liabilities and common stockholders' equity	$ 8,772,719	$ 7,098,438