REGULATORY ACTIONS, Deferred Energy (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	$ (260,079)
Amortization	77,059
Deferred Energy Over Collections	(64,975)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(247,995)
Reinstatement of deferred energy (effective 6/07, 10 years)	114,490
Total Deferred Energy	(133,505)
Deferred Assets
Deferred energy	99,566		102,525
Current Liabilities
Deferred Energy Liability	233,071		245,164
NPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(174,714)
Amortization	38,126
Deferred Energy Over Collections	(39,226)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(175,814)
Reinstatement of deferred energy (effective 6/07, 10 years)	114,490
Total Deferred Energy	(61,324)
Deferred Assets
Deferred energy	99,566
Current Liabilities
Deferred Energy Liability	(160,890)
SPPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(56,337)
Amortization	25,498
Deferred Energy Over Collections	(13,213)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(44,052)
Reinstatement of deferred energy (effective 6/07, 10 years)
Total Deferred Energy	(44,052)
Current Liabilities
Deferred Energy Liability	(44,052)
SPPC Gas [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(29,028)
Amortization	13,435
Deferred Energy Over Collections	(12,536)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(28,129)
Reinstatement of deferred energy (effective 6/07, 10 years)
Total Deferred Energy	(28,129)
Current Liabilities
Deferred Energy Liability	$ (28,129)

[1] These deferred energy over collections are subject to quarterly rate resets as discussed in Note 3, Regulatory Actions, of the Notes to Financial Statements in the 2011 Form 10-K.