SCHEDULE I - Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities:
Net Income	$ 179,200	$ 211,400	$ 173,100	$ 230,000	$ 176,600	$ 209,500	$ 46,200	$ 100,800	$ 793,689	$ 533,077	$ 400,513
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Deferred Income Tax Expense (Benefit)									431,413	292,000	196,761
Other Noncash Income (Expense)									56,071	42,852	(48,772)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net									163,549	20,214	(17,570)
Change in Accounts Payable									(54,619)	(128,339)	18,916
Taxes Receivable/(Accrued)									50,950	5,450	(49,642)
Other Current Assets and Liabilities									22,623	(8,532)	(12,569)
Net Cash Flows Provided by Operating Activities									1,663,539	1,161,229	970,386
Investing Activities:
Other Investing Activities									(67,816)	(35,683)	(60,674)
Net Cash Flows Used in Investing Activities									(1,441,223)	(1,467,924)	(1,018,587)
Financing Activities:
Cash Dividends on Common Stock									462,741	375,047	194,555
Increase/(Decrease) in Short-Term Debt									(397,000)	825,000	50,000
Issuance of Long-Term Debt									1,680,000	850,000	627,500
Retirements of Long-Term Debt									929,885	839,136	369,586
Other Financing Activities									(25,253)	6,529	(7,123)
Net Cash Flows Provided by/(Used in) Financing Activities									(224,700)	345,884	31,365
Supplemental Cash Flow Information [Abstract]
Interest Paid, Net of Amounts Capitalized									343,300	356,500	256,300
Income Taxes Paid									50,000	(12,800)	(76,600)
Net Increase/(Decrease) in Cash									(2,384)	39,189	(16,836)
Cash - Beginning of Year				45,748				6,559	45,748	6,559	23,395
Cash - End of Year	43,364				45,748				43,364	45,748	6,559
Nu Parent [Member]
Operating Activities:
Net Income									786,007	526,048	394,955
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity In Earnings of Subsidiaries									(785,650)	(579,221)	(422,408)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries									407,837	374,584	389,292
Deferred Income Tax Expense (Benefit)									15,159	(15,350)	(15,934)
Other Noncash Income (Expense)									29,169	(3,755)	33,238
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net									14,704	(18,321)	(436)
Change in Accounts Payable									(7,058)	48,332	(183)
Taxes Receivable/(Accrued)									13,295	(16,872)	11,537
Other Current Assets and Liabilities									(1,411)	60,182	484
Net Cash Flows Provided by Operating Activities									472,052	375,627	390,545
Investing Activities:
Capital Contributions To Subsidiaries									(65,400)	(81,431)	(233,349)
Return Of Investment In Subsidiaries									0	8,207	0
(Increase) Decrease in Due from Related Parties									0	2,200	400
(Increase) Decrease In Notes Receivable From Affiliated Company									5,475	(704,475)	19,000
Other Investing Activities									(1,862)	(608)	(2,585)
Net Cash Flows Used in Investing Activities									(61,787)	(776,107)	(216,534)
Financing Activities:
Cash Dividends on Common Stock									462,741	375,047	194,555
Increase/(Decrease) in Short-Term Debt									(135,500)	733,500	19,000
Issuance of Long-Term Debt									750,000	300,000	0
Retirements of Long-Term Debt									(550,000)	(263,000)	0
Other Financing Activities									(12,418)	5,394	1,338
Net Cash Flows Provided by/(Used in) Financing Activities									(410,659)	400,847	(174,217)
Supplemental Cash Flow Information [Abstract]
Interest Paid, Net of Amounts Capitalized									33,822	50,144	24,951
Income Taxes Paid									(30,603)	(27,126)	(10,833)
Net Increase/(Decrease) in Cash									(394)	367	(206)
Cash - Beginning of Year				429				62	429	62	268
Cash - End of Year	$ 35				$ 429				$ 35	$ 429	$ 62