SCHEDULE I - Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Current Assets:
Cash	$ 6,559	$ 23,395	$ 26,952	$ 89,816
Receivables, Net	488,002	523,644
Taxes Receivable	4,931	89,638
Prepayments and Other Current Assets	107,701	100,441
Total Current Assets	1,357,472	1,507,000
Deferred Debits and Other Assets:
Equity Method Investments	2,100	2,000
Derivative Assets Noncurrent	98,357	123,242
Other Long-Term Assets	172,560	179,261
Total Deferred Debits and Other Assets	3,886,529	3,397,875
Total Assets	15,647,066	14,472,601
Current Liabilities:
Notes Payable to Banks	317,000	267,000
Long-Term Debt - Current Portion	331,582	66,286
Accounts Payable - Current	633,282	417,285
Accrued Taxes	69,592	107,067
Accrued Interest	69,198	74,740
Other Liabilities - Current	176,558	167,206
Total Current Liabilities	1,947,682	1,345,147
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	420,011	447,496
Total Deferred Credits and Other Liabilities	4,840,385	4,384,183
Capitalization:
Long-Term Debt	4,614,913	4,632,866
Common Shareholders' Equity:
Common Stock	980,264	978,909
Capital Surplus, Paid In	1,797,884	1,777,592
Retained Earnings	1,651,875	1,452,777
Accumulated Other Comprehensive Loss	70,686	43,370
Treasury Stock	(346,667)	(354,732)
Common Shareholders' Equity	4,012,670	3,811,176
Noncontrolling Interest	2,956	1,457
Total Equity	4,015,626	3,812,633
Total Capitalization	8,746,739	8,561,699
Total Liabilities and Capitalization	15,647,066	14,472,601
Nu Parent [Member]
Current Assets:
Cash	62	268	1,222	1,294
Notes Receivable from Affiliated Companies	113,200	132,600
Receivables, Net	2,735	2,885
Accounts Receivable from Affiliated Companies	1,749	1,163
Taxes Receivable	5,308	18,139
Prepayments and Other Current Assets	4,610	18,021
Total Current Assets	127,664	173,076
Deferred Debits and Other Assets:
Equity Method Investments	4,566,865	4,323,455
Notes Receivable, Related Parties, Noncurrent	62,500	62,500
Deferred Tax Assets, Net, Noncurrent	39,405	23,288
Derivative Assets Noncurrent	0	4,099
Other Long-Term Assets	9,979	8,179
Total Deferred Debits and Other Assets	4,678,749	4,421,521
Total Assets	4,806,413	4,594,597
Current Liabilities:
Notes Payable to Banks	256,000	237,000
Long-Term Debt - Current Portion	265,296	0
Accounts Payable - Current	266	179
Accounts Payable to Affiliated Companies	141	411
Accrued Taxes	0	3,616
Accrued Interest	8,735	8,024
Other Liabilities - Current	865	1,145
Total Current Liabilities	531,303	250,375
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	9,511	6,776
Total Deferred Credits and Other Liabilities	9,511	6,776
Capitalization:
Long-Term Debt	249,973	524,813
Common Shareholders' Equity:
Common Stock	980,264	978,909
Capital Surplus, Paid In	1,797,884	1,777,592
Retained Earnings	1,651,875	1,452,777
Accumulated Other Comprehensive Loss	(70,686)	(43,370)
Treasury Stock	(346,667)	(354,732)
Common Shareholders' Equity	4,012,670	3,811,176
Noncontrolling Interest	2,956	1,457
Total Equity	4,015,626	3,812,633
Total Capitalization	4,265,599	4,337,446
Total Liabilities and Capitalization	$ 4,806,413	$ 4,594,597