FAIR VALUE (Details 2) (Nonregulated Segments, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Natural gas contracts
Transfers between the levels of the fair value hierarchy
Transfers into Level 2 from Level 3		$ 1.3
Transfers into Level 3 from Level 2	0.2	2.4
Electric contracts
Transfers between the levels of the fair value hierarchy
Transfers into Level 2 from Level 3	5.5	(0.1)
Transfers into Level 3 from Level 2		$ (5.0)