ASSETS HELD FOR SALE (Details) (USD $)	12 Months Ended				1 Months Ended					1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 NPC [Member]	Dec. 31, 2010 NPC [Member]	Aug. 31, 2011 NPC [Member] Telecommunication Towers [Member] number	Dec. 31, 2011 SPPC [Member]	Dec. 31, 2010 SPPC [Member]	Dec. 31, 2011 SPPC [Member] Electric Distribution and Generation Assets [Member]	Dec. 31, 2010 SPPC [Member] Electric Distribution and Generation Assets [Member]	May 31, 2010 SPPC [Member] Independence Lake [Member]
Long Lived Assets Held-for-sale [Line Items]
Number of towers sold					37
Long Lived Assets Held-for-sale, Proceeds from Sale					$ 32,000,000			$ 132,000,000		$ 15,000,000
Assets
Utility Plant in Service									196,800,000
Less: Accumulated depreciation	3,184,071,000	3,047,438,000	1,906,617,000	1,828,366,000		1,277,454,000	1,219,072,000		55,800,000
Public Utilities, Property, Plant and Equipment, Net	9,227,073,000	8,929,659,000	6,791,695,000	6,548,810,000		2,435,378,000	2,380,849,000		141,000,000
CWIP	487,427,000	908,579,000	352,541,000	825,079,000		134,886,000	83,500,000		5,200,000
Other Assets Held-for-sale, Current									9,100,000
Assets Held-for-sale, Long Lived	0	155,322,000				0	155,322,000		155,300,000
Liabilities
Deferred Credits and Other Liabilities, Noncurrent									30,700,000
Liabilities Held for Sale	0	30,706,000				0	30,706,000		30,700,000
Gain (Loss) on Sale of Properties, before Applicable Income Taxes										14,700,000
Deferred gain recorded as a regulatory liability										$ 7,100,000
Amortization period (in years)	Various									three