REGULATORY ACTIONS, Summary of Regulatory Actions (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
SPPC Gas [Member]
DEAA Filings [Abstract]
Requested rate increase (decrease)	$ 0.2
NPC [Member]
Summary of Rate Filings [Line Items]
Amount Of gain approved by PUCN	27.3
Gain on Sale of Telecommunications Towers	32.0
Revenue Requirement Subject To Change:
Requested and Amended Revenue Requirement	120.0
Present Revenue Requirement	126.6
$ Change in Revenue Requirement	(6.6)
NPC [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Oct. 2012	[1]
Requested and Amended Revenue Requirement	13.1	[1]
Present Revenue Requirement	0	[1]
$ Change in Revenue Requirement	13.1	[1]
NPC [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Oct. 2012
Requested and Amended Revenue Requirement	28.2
Present Revenue Requirement	8.5
$ Change in Revenue Requirement	19.7
NPC [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Oct. 2012
Requested and Amended Revenue Requirement	15.3
Present Revenue Requirement	18.0
$ Change in Revenue Requirement	(2.7)
NPC [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	33.1
Present Revenue Requirement	57.3
$ Change in Revenue Requirement	(24.2)
NPC [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	8.9
Present Revenue Requirement	21.2
$ Change in Revenue Requirement	(12.3)
NPC [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	11.0
Present Revenue Requirement	16.8
$ Change in Revenue Requirement	(5.8)
NPC [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	10.4
Present Revenue Requirement	4.8
$ Change in Revenue Requirement	5.6
SPPC [Member] | SPPC Electric [Member]
Revenue Requirement Subject To Change:
Requested and Amended Revenue Requirement	54.5
Present Revenue Requirement	65.8
$ Change in Revenue Requirement	(11.3)
SPPC [Member] | SPPC Electric [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Oct. 2012
Requested and Amended Revenue Requirement	34.5
Present Revenue Requirement	38.5
$ Change in Revenue Requirement	(4.0)
SPPC [Member] | SPPC Electric [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Oct. 2012
Requested and Amended Revenue Requirement	6.1
Present Revenue Requirement	9.2
$ Change in Revenue Requirement	(3.1)
SPPC [Member] | SPPC Electric [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	5.4
Present Revenue Requirement	9.8
$ Change in Revenue Requirement	(4.4)
SPPC [Member] | SPPC Electric [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	1.7
Present Revenue Requirement	4.7
$ Change in Revenue Requirement	(3.0)
SPPC [Member] | SPPC Electric [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	4.9
Present Revenue Requirement	3.1
$ Change in Revenue Requirement	1.8
SPPC [Member] | SPPC Electric [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Anticipated Effective Date	Jan. 2013
Requested and Amended Revenue Requirement	1.9
Present Revenue Requirement	0.5
$ Change in Revenue Requirement	$ 1.4

[1] This rate request represents revenues previously recorded as a result of NPC's 2008 GRC. As such, NPC will not record furtherrevenue related to this rate request, but does expect to collect such amounts from its customers. Reference Note 3, Regulatory Actions, NPC 2008 GRC, of the Notes to Financial Statements in the 2011 Form 10-K.