LONG-TERM DEBT, Debt Instruments (Details) (USD $) In Thousands, unless otherwise specified			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended			12 Months Ended						12 Months Ended				12 Months Ended				12 Months Ended																				12 Months Ended		12 Months Ended											12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Secured General And Refunding Mortgage Securities Npc Series [Member]	Dec. 31, 2010 Secured General And Refunding Mortgage Securities Npc Series [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series I [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series I [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series L [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series L [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series M [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series M [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series N [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series N [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series O [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series O [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series R [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series R [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, NPC Series S [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, NPC Series S [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, Series U [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, Series U [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, Series V [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, Series V [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, Series X [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, Series X [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, Series Y [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, SPPC Series M [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, SPPC Series M [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, SPPC Series P [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, SPPC Series P [Member]	Dec. 31, 2011 Secured, General and Refunding Mortgage Securities, SPPC Series Q [Member]	Dec. 31, 2010 Secured, General and Refunding Mortgage Securities, SPPC Series Q [Member]	Dec. 31, 2011 Secured Variable Rate Debt Npc Idrb Series 2000 A [Member]	Dec. 31, 2010 Secured Variable Rate Debt Npc Idrb Series 2000 A [Member]	Dec. 31, 2011 Secured Variable Rate Debt, NPC PCRB Series 2006 [Member]	Dec. 31, 2010 Secured Variable Rate Debt, NPC PCRB Series 2006 [Member]	Dec. 31, 2011 Secured Variable Rate Debt Npc Pcrb Series 2006 A [Member]	Dec. 31, 2010 Secured Variable Rate Debt Npc Pcrb Series 2006 A [Member]	Dec. 31, 2011 Secured Variable Rate Debt Sppc Pcrb Series 2006 A [Member]	Dec. 31, 2010 Secured Variable Rate Debt Sppc Pcrb Series 2006 A [Member]	Dec. 31, 2011 Secured Variable Rate Debt Sppc Pcrb Series 2006 B [Member]	Dec. 31, 2010 Secured Variable Rate Debt Sppc Pcrb Series 2006 B [Member]	Dec. 31, 2011 Secured Variable Rate Debt Sppc Pcrb Series 2006 C [Member]	Dec. 31, 2010 Secured Variable Rate Debt Sppc Pcrb Series 2006 C [Member]	Dec. 31, 2010 Secured Variable Rate Debt, Revolving Credit Facilities [Member]	Dec. 31, 2011 NVE Senior Notes due 2014 [Member]	Dec. 31, 2011 NVE Senior Notes due 2017 [Member]	Dec. 31, 2010 NVE Senior Notes due 2017 [Member]	Dec. 31, 2011 NVE Senior Notes due 2020 [Member]	Dec. 31, 2010 NVE Senior Notes due 2020 [Member]	Dec. 31, 2011 Obligations under capital leases [Member]	Dec. 31, 2010 Obligations under capital leases [Member]	Dec. 31, 2011 NVE [Member]	Dec. 31, 2010 NVE [Member]	Dec. 31, 2010 NVE [Member] NVE Senior Notes due 2012 [Member]	Dec. 31, 2010 NVE [Member] NVE Senior Notes due 2014 [Member]	Dec. 31, 2011 NVE [Member] NVE Senior Notes due 2014 [Member]	Dec. 31, 2010 NVE [Member] NVE Senior Notes due 2017 [Member]	Dec. 31, 2010 NVE [Member] NVE Senior Notes due 2020 [Member]	Dec. 31, 2011 NVE [Member] NVE Senior Notes due 2020 [Member]	Dec. 31, 2011 NPC [Member]	Dec. 31, 2010 NPC [Member]	Dec. 31, 2011 NPC [Member] Secured General And Refunding Mortgage Securities Npc Series [Member]	Dec. 31, 2010 NPC [Member] Secured General And Refunding Mortgage Securities Npc Series [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series I [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series I [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series L [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series L [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series M [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series M [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series N [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series N [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series O [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series O [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series R [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series R [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series S [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, NPC Series S [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, Series U [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, Series U [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, Series V [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, Series V [Member]	Dec. 31, 2010 NPC [Member] Secured, General and Refunding Mortgage Securities, Series X [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, Series X [Member]	Dec. 31, 2011 NPC [Member] Secured, General and Refunding Mortgage Securities, Series Y [Member]	Dec. 31, 2011 NPC [Member] Secured Variable Rate Debt Npc Idrb Series 2000 A [Member]	Dec. 31, 2010 NPC [Member] Secured Variable Rate Debt Npc Idrb Series 2000 A [Member]	Dec. 31, 2011 NPC [Member] Secured Variable Rate Debt, NPC PCRB Series 2006 [Member]	Dec. 31, 2010 NPC [Member] Secured Variable Rate Debt, NPC PCRB Series 2006 [Member]	Dec. 31, 2011 NPC [Member] Secured Variable Rate Debt Npc Pcrb Series 2006 A [Member]	Dec. 31, 2010 NPC [Member] Secured Variable Rate Debt Npc Pcrb Series 2006 A [Member]	Dec. 31, 2011 NPC [Member] Obligations under capital leases [Member]	Dec. 31, 2010 NPC [Member] Obligations under capital leases [Member]	Dec. 31, 2011 SPPC [Member]	Dec. 31, 2010 SPPC [Member]	Dec. 31, 2010 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series H [Member]	Dec. 31, 2011 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series M [Member]	Dec. 31, 2010 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series M [Member]	Dec. 31, 2011 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series P [Member]	Dec. 31, 2010 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series P [Member]	Dec. 31, 2011 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series Q [Member]	Dec. 31, 2010 SPPC [Member] Secured, General and Refunding Mortgage Securities, SPPC Series Q [Member]	Dec. 31, 2011 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 A [Member]	Dec. 31, 2010 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 A [Member]	Dec. 31, 2011 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 B [Member]	Dec. 31, 2010 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 B [Member]	Dec. 31, 2011 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 C [Member]	Dec. 31, 2010 SPPC [Member] Secured Variable Rate Debt Sppc Pcrb Series 2006 C [Member]	Dec. 31, 2010 SPPC [Member] Secured Variable Rate Debt, Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities	$ 5,161,462			$ 350,000	$ 130,000	$ 130,000	$ 250,000	$ 250,000	$ 210,000	$ 210,000	$ 370,000	$ 370,000	$ 325,000	$ 325,000	$ 350,000	$ 350,000	$ 500,000	$ 500,000	$ 125,000	$ 125,000	$ 500,000	$ 500,000	$ 250,000	$ 250,000	$ 250,000	$ 450,000	$ 450,000	$ 251,742	$ 251,742	$ 250,000	$ 250,000	$ 98,100	$ 98,100	$ 37,700	$ 37,700	$ 37,975	$ 37,975	$ 58,200	$ 58,200	$ 75,000	$ 75,000	$ 81,475	$ 81,475	$ 15,000	$ 195,000		$ 191,500	$ 315,000	$ 315,000	$ 51,270	$ 55,735	$ 510,000				$ 195,000	$ 191,500	$ 315,000	$ 315,000	$ 3,485,045			$ 350,000	$ 130,000	$ 130,000	$ 250,000	$ 250,000	$ 210,000	$ 210,000	$ 370,000	$ 370,000	$ 325,000	$ 325,000	$ 350,000	$ 350,000	$ 500,000	$ 500,000	$ 125,000	$ 125,000	$ 500,000	$ 500,000	$ 250,000	$ 250,000	$ 250,000	$ 98,100	$ 98,100	$ 37,700	$ 37,700	$ 37,975	$ 37,975	$ 51,270	$ 55,735	$ 1,166,417			$ 450,000	$ 450,000	$ 251,742	$ 251,742	$ 250,000	$ 250,000	$ 58,200	$ 58,200	$ 75,000	$ 75,000	$ 81,475	$ 81,475	$ 15,000
Debt Instrument, Unamortized Discount (Premium), Net	12,546	(2,611)																																																			(1)							25,455	11,748																																(12,909)	(14,358)
Current maturities	(139,985)	(355,929)																																																										(139,985)	(355,929)																																0	0
Total Long-Term Debt	$ 5,008,931	$ 4,924,109																																																										$ 3,319,605	$ 3,221,833																																$ 1,179,326	$ 1,195,775
Stated interest rate (in hundredths)			8.25%		6.50%		5.875%		5.95%		6.65%		6.50%		6.75%		6.50%		7.375%		7.125%		5.375%		5.45%	6.00%		6.75%		5.45%															2.81%	6.75%		6.25%
Maturity date			2011		2012		2015		2016		2036		2018		2037		2018		2014		2019		2040		2041	2016		2037		2013		2020		2036		2032		2031		2036		2036			2014	2017		2020						2012	2014			2020				June 1, 2011																				2040		May 15, 2041											2012