FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fair value of consolidated long-term debt	$ 6,000,000,000	$ 5,700,000,000
NPC [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fair value of consolidated long-term debt	4,100,000,000	3,900,000,000
SPPC [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fair value of consolidated long-term debt	$ 1,300,000,000	$ 1,300,000,000