SCHEDULE I - Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current Assets:
Cash	$ 45,748	$ 6,559	$ 23,395	$ 26,952
Receivables, Net	792,822	488,002
Prepayments and Other Current Assets	107,972	112,632
Total Current Assets	2,227,295	1,357,472
Deferred Debits and Other Assets:
Derivative Assets Noncurrent	90,612	98,357
Other Long-Term Assets	327,766	172,560
Total Deferred Debits and Other Assets	9,470,519	3,886,529
Total Assets	28,302,824	15,647,066
Current Liabilities:
Notes Payable to Banks	1,120,196	317,000
Long-Term Debt - Current Portion	763,338	331,582
Accounts Payable - Current	764,350	633,282
Other Liabilities - Current	744,497	390,416
Total Current Liabilities	3,643,690	1,947,682
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	967,561	420,011
Total Deferred Credits and Other Liabilities	7,984,221	4,840,385
Capitalization:
Long-Term Debt	7,200,156	4,614,913
Common Shareholders' Equity:
Common Stock	1,662,547	980,264
Capital Surplus, Paid In	6,183,267	1,797,884
Retained Earnings	1,802,714	1,651,875
Accumulated Other Comprehensive Loss	72,854	70,686
Treasury Stock	(338,624)	(346,667)
Common Shareholders' Equity	9,237,050	4,012,670
Noncontrolling Interest	0	2,956
Total Equity	9,237,050	4,015,626
Total Capitalization	16,592,774	8,746,739
Total Liabilities and Capitalization	28,302,824	15,647,066
Nu Parent [Member]
Current Assets:
Cash	250	62	268	1,222
Notes Receivable from Affiliated Companies	1,025,000	113,200
Receivables, Net	1	2,735
Accounts Receivable from Affiliated Companies	11,173	1,749
Taxes Receivable	11,220	5,308
Prepayments and Other Current Assets	2,665	4,610
Total Current Assets	1,050,309	127,664
Deferred Debits and Other Assets:
Equity Method Investments	9,874,692	4,566,865
Notes Receivable, Related Parties, Noncurrent	25,000	62,500
Deferred Tax Assets, Net, Noncurrent	67,619	39,405
Other Long-Term Assets	12,597	9,979
Total Deferred Debits and Other Assets	9,979,908	4,678,749
Total Assets	11,030,217	4,806,413
Current Liabilities:
Notes Payable to Banks	1,150,000	256,000
Long-Term Debt - Current Portion	549,992	265,296
Accounts Payable - Current	9,854	266
Accounts Payable to Affiliated Companies	27,559	141
Accrued Taxes	7,509	0
Accrued Interest	4,943	8,735
Other Liabilities - Current	26,825	865
Total Current Liabilities	1,776,682	531,303
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	16,485	9,511
Total Deferred Credits and Other Liabilities	16,485	9,511
Capitalization:
Long-Term Debt	0	249,973
Common Shareholders' Equity:
Common Stock	1,662,547	980,264
Capital Surplus, Paid In	6,183,267	1,797,884
Retained Earnings	1,802,714	1,651,875
Accumulated Other Comprehensive Loss	(72,854)	(70,686)
Treasury Stock	(338,624)	(346,667)
Common Shareholders' Equity	9,237,050	4,012,670
Noncontrolling Interest	0	2,956
Total Equity	9,237,050	4,015,626
Total Capitalization	9,237,050	4,265,599
Total Liabilities and Capitalization	$ 11,030,217	$ 4,806,413