DISPOSITIONS - DISPOSITIONS EXCLUDING DISCONTINUED OPERATIONS (Details) $ in Millions	1 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2015 USD ($)	Aug. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)
Disclosures related to the disposal
Pre-tax gain on sale				$ 6.1	$ 0.0
Assets and liabilities included in the sale
Total assets	$ 0.0		$ 0.0	0.0			$ 51.5
Total liabilities	$ 0.0		0.0	$ 0.0			13.8
Corporate and Other | PDL solar power generation plants
Disclosures related to the disposal
Number of solar power generation plants sold	48
Proceeds from sale	$ 47.8
Pre-tax gain on sale			5.2
Transaction costs			$ 0.9
Assets and liabilities included in the sale
Cash and cash equivalents						$ 0.3	0.0
Accounts receivable						0.7	0.0
Property, plant, and equipment, net of accumulated depreciation						31.1	32.1
Accumulated depreciation						22.1	21.1
Other long-term assets						17.9	19.4
Total assets						50.0	51.5
Current liabilities						0.3	0.3
Deferred investment tax credits						4.6	5.0
Asset retirement obligations						1.1	1.1
Other long-term liabilities						6.8	7.4
Total liabilities						$ 12.8	$ 13.8
Other States | UPPCO
Disclosures related to the disposal
Proceeds from sale		$ 336.7
Other States | UPPCO | Minimum
Disclosures related to the disposal
Transition period for services		18 months
Other States | UPPCO | Maximum
Disclosures related to the disposal
Transition period for services		30 months