SCHEDULE I - Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current Assets:
Cash	$ 38,703	$ 43,364	$ 45,748	$ 6,559
Receivables, Net	856,346	765,391
Taxes Receivable	337,307	16,629
Prepayments and Other Current Assets	226,194	197,659
Total Current Assets	2,692,465	2,087,049
Deferred Debits and Other Assets:
Other Long-Term Assets	349,957	365,692
Total Deferred Debits and Other Assets	8,438,469	8,132,302
Goodwill	3,519,401	3,519,401
Total Assets	29,777,975	27,795,537
Current Liabilities:
Notes Payable	956,825	1,093,000
Long-Term Debt - Current Portion	245,583	533,346
Accounts Payable - Current	868,231	742,251
Other Liabilities - Current	828,720	702,776
Total Current Liabilities	3,134,381	3,275,651
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	874,387	923,053
Total Deferred Credits and Other Liabilities	7,905,194	6,975,957
Capitalization:
Long-Term Debt	8,606,017	7,776,833
Common Shareholders' Equity:
Common Stock	1,666,796	1,665,351
Capital Surplus, Paid In	6,235,834	6,192,765
Retained Earnings	2,448,661	2,125,980
Accumulated Other Comprehensive Loss	(74,009)	(46,031)	(72,900)
Treasury Stock	(300,467)	(326,537)
Common Shareholders' Equity	9,976,815	9,611,528
Total Capitalization	18,738,400	17,543,929
Total Liabilities and Capitalization	29,777,975	27,795,537
Nu Parent [Member]
Current Assets:
Cash	138	35	429	62
Notes Receivable from Affiliated Companies	741,150	871,050
Accounts Receivable from Affiliated Companies	6,725	95,513
Prepayments and Other Current Assets	41,366	59,905
Total Current Assets	789,379	1,026,503
Deferred Debits and Other Assets:
Equity Method Investments	8,387,976	7,733,051
Notes Receivable, Related Parties, Noncurrent	106,300	62,500
Deferred Tax Assets, Net, Noncurrent	177,908	205,779
Other Long-Term Assets	33,552	22,099
Total Deferred Debits and Other Assets	11,937,547	11,255,240
Goodwill	3,231,811	3,231,811
Total Assets	12,726,926	12,281,743
Current Liabilities:
Notes Payable	654,825	1,014,500
Long-Term Debt - Current Portion	28,883	31,696
Accounts Payable - Current	141	441
Accounts Payable to Affiliated Companies	150,268	144,026
Other Liabilities - Current	71,778	59,559
Total Current Liabilities	905,895	1,250,222
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	125,608	122,226
Total Deferred Credits and Other Liabilities	125,608	122,226
Capitalization:
Long-Term Debt	1,718,608	1,297,767
Common Shareholders' Equity:
Common Stock	1,666,796	1,665,351
Capital Surplus, Paid In	6,235,834	6,192,765
Retained Earnings	2,448,661	2,125,980
Accumulated Other Comprehensive Loss	(74,009)	(46,031)
Treasury Stock	(300,467)	(326,537)
Common Shareholders' Equity	9,976,815	9,611,528
Total Capitalization	11,695,423	10,909,295
Total Liabilities and Capitalization	$ 12,726,926	$ 12,281,743