REGULATORY MATTERS (Details 4) (USD $)		0 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2012	Apr. 28, 2009 SPP Day-Ahead Market Electric item	Dec. 31, 2012 SPP Regional Transmission Development Electric	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects 300 kV or larger Electric	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects 300 kV or larger Electric Minimum kV	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects between 100 kV and 300 kV Electric	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects between 100 kV and 300 kV Electric Maximum kV	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects between 100 kV and 300 kV Electric Minimum kV	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects under 100 kV Electric	Apr. 30, 2010 SPP Regional Transmission Development Transmission projects under 100 kV Electric Maximum kV
RATE MATTERS
Number of state commissions		4
Amount approved in highway/byway projects to be constructed over the next several years			$ 2,800,000,000
Expected additional amount approval in highway/byway projects to be constructed over the next several years			745,000,000
Deferred expenses related to rate cases	$ 1,800,000
Capacity of transmission projects funded by region (in kV)					300		300	100		100
Percentage of funding by region for transmission projects				100.00%		33.00%
Percentage of funding by individual constructing zones for transmission projects						67.00%			100.00%