DEBT COVENANT AND OTHER RESTRICTIONS, Dividends (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended						3 Months Ended								12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 NPC [Member]	Dec. 31, 2011 SPPC [Member]	Dec. 31, 2011 NVE [Member]	Sep. 30, 2011 NVE [Member]	Jun. 30, 2011 NVE [Member]	Mar. 31, 2011 NVE [Member]	Dec. 31, 2010 NVE [Member]	Sep. 30, 2010 NVE [Member]	Jun. 30, 2010 NVE [Member]	Mar. 31, 2010 NVE [Member]	Dec. 31, 2011 NVE [Member]
Dividends [Abstract]
Dividend declaration date					Feb. 10, 2012	Feb. 10, 2012									Feb. 10, 2012
Dividend declared to parent company						$ 20									$ 39
Common Stock, Dividends, Per Share, Declared	$ 0.49	$ (115,587,000.00)	$ 0.45	$ 0.41			$ 0.13	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.11	$ 0.11	$ 0.11
Dividends Payable, Date of Record, Day, Month and Year															Mar. 06, 2012