COMMON STOCK AND OTHER PAID IN CAPITAL (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Dividends Payable [Line Items]
Dividends Declared Per Share of Common Stock	$ 0.17	$ 0.12	$ 0.30	$ 0.24
NVE [Member] | First Declaration [Member]
Dividends Payable [Line Items]
Dividends Declared Per Share of Common Stock			$ 0.13
Dividends [Abstract]
Declaration date			Feb. 10, 2012
Dividends Payable, Date to be Paid, Day, Month and Year			Mar. 21, 2012
Dividends Payable, Date of Record, Day, Month and Year			Mar. 06, 2013
NVE [Member] | Second Declaration [Member]
Dividends Payable [Line Items]
Dividends Declared Per Share of Common Stock			$ 0.17
Dividends [Abstract]
Declaration date			May 07, 2012
Dividends Payable, Date to be Paid, Day, Month and Year			Jun. 20, 2012
Dividends Payable, Date of Record, Day, Month and Year			Jun. 05, 2012
NVE [Member] | Third Declaration [Member]
Dividends Payable [Line Items]
Dividends Declared Per Share of Common Stock			$ 0.17
Dividends [Abstract]
Declaration date			Aug. 02, 2012
Dividends Payable, Date to be Paid, Day, Month and Year			Sep. 19, 2012
Dividends Payable, Date of Record, Day, Month and Year			Sep. 04, 2012
NPC [Member]
Dividends [Abstract]
Declaration date			Aug. 02, 2012
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries			$ 79.0
Dividend declared to parent company			40.0
SPPC [Member]
Dividends [Abstract]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries			$ 20.0