FAIR VALUE (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets
Risk Management Assets	$ 315.5	$ 190.7
Liabilities
Risk Management Liabilities	226.6	240.3
Fair value measurements on a recurring basis | Level 1
Assets
Risk Management Assets	83.9	70.3
Liabilities
Risk Management Liabilities	113.6	73.7
Fair value measurements on a recurring basis | Level 2
Assets
Risk Management Assets	177.8	100.8
Liabilities
Risk Management Liabilities	81.3	142.1
Fair value measurements on a recurring basis | Level 3
Assets
Risk Management Assets	53.8	19.6
Liabilities
Risk Management Liabilities	31.7	24.5
Fair value measurements on a recurring basis | Total, Fair value
Assets
Risk Management Assets	315.5	190.7
Liabilities
Risk Management Liabilities	226.6	240.3
Fair value measurements on a recurring basis | Utility segments | Natural gas contracts | Level 1
Assets
Risk Management Assets	2.4	0.3
Liabilities
Risk Management Liabilities	0.5	1.1
Fair value measurements on a recurring basis | Utility segments | Natural gas contracts | Level 2
Assets
Risk Management Assets	7.7	3.1
Liabilities
Risk Management Liabilities	0.6	14.1
Fair value measurements on a recurring basis | Utility segments | Natural gas contracts | Level 3
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Fair value measurements on a recurring basis | Utility segments | Natural gas contracts | Total, Fair value
Assets
Risk Management Assets	10.1	3.4
Liabilities
Risk Management Liabilities	1.1	15.2
Fair value measurements on a recurring basis | Utility segments | FTRs | Level 1
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Fair value measurements on a recurring basis | Utility segments | FTRs | Level 2
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Fair value measurements on a recurring basis | Utility segments | FTRs | Level 3
Assets
Risk Management Assets	2.1	2.1
Liabilities
Risk Management Liabilities	0.3	0.1
Fair value measurements on a recurring basis | Utility segments | FTRs | Total, Fair value
Assets
Risk Management Assets	2.1	2.1
Liabilities
Risk Management Liabilities	0.3	0.1
Fair value measurements on a recurring basis | Utility segments | Petroleum product contracts | Level 1
Assets
Risk Management Assets	0.1	0.2
Fair value measurements on a recurring basis | Utility segments | Petroleum product contracts | Level 2
Assets
Risk Management Assets	0	0
Fair value measurements on a recurring basis | Utility segments | Petroleum product contracts | Level 3
Assets
Risk Management Assets	0	0
Fair value measurements on a recurring basis | Utility segments | Petroleum product contracts | Total, Fair value
Assets
Risk Management Assets	0.1	0.2
Fair value measurements on a recurring basis | Utility segments | Coal contracts | Level 1
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Fair value measurements on a recurring basis | Utility segments | Coal contracts | Level 2
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Fair value measurements on a recurring basis | Utility segments | Coal contracts | Level 3
Assets
Risk Management Assets	0.2	2.5
Liabilities
Risk Management Liabilities	2.7	9.0
Fair value measurements on a recurring basis | Utility segments | Coal contracts | Total, Fair value
Assets
Risk Management Assets	0.2	2.5
Liabilities
Risk Management Liabilities	2.7	9.0
Fair value measurements on a recurring basis | Nonregulated segments | Level 1
Assets
Investment in exchange-traded funds	15.9	11.8
Liabilities
Contingent Consideration	0
Fair value measurements on a recurring basis | Nonregulated segments | Level 2
Assets
Investment in exchange-traded funds	0	0
Liabilities
Contingent Consideration	0
Fair value measurements on a recurring basis | Nonregulated segments | Level 3
Assets
Investment in exchange-traded funds	0	0
Liabilities
Contingent Consideration	7.8
Fair value measurements on a recurring basis | Nonregulated segments | Total, Fair value
Assets
Investment in exchange-traded funds	15.9	11.8
Liabilities
Contingent Consideration	7.8
Fair value measurements on a recurring basis | Nonregulated segments | Natural gas contracts | Level 1
Assets
Risk Management Assets	16.3	21.4
Liabilities
Risk Management Liabilities	14.3	17.7
Fair value measurements on a recurring basis | Nonregulated segments | Natural gas contracts | Level 2
Assets
Risk Management Assets	35.2	36.4
Liabilities
Risk Management Liabilities	22.0	36.9
Fair value measurements on a recurring basis | Nonregulated segments | Natural gas contracts | Level 3
Assets
Risk Management Assets	35.6	5.4
Liabilities
Risk Management Liabilities	25.2	1.5
Fair value measurements on a recurring basis | Nonregulated segments | Natural gas contracts | Total, Fair value
Assets
Risk Management Assets	87.1	63.2
Liabilities
Risk Management Liabilities	61.5	56.1
Fair value measurements on a recurring basis | Nonregulated segments | Electric contracts | Level 1
Assets
Risk Management Assets	65.1	48.4
Liabilities
Risk Management Liabilities	98.8	54.9
Fair value measurements on a recurring basis | Nonregulated segments | Electric contracts | Level 2
Assets
Risk Management Assets	134.9	61.3
Liabilities
Risk Management Liabilities	58.7	91.1
Fair value measurements on a recurring basis | Nonregulated segments | Electric contracts | Level 3
Assets
Risk Management Assets	15.9	9.6
Liabilities
Risk Management Liabilities	3.5	13.9
Fair value measurements on a recurring basis | Nonregulated segments | Electric contracts | Total, Fair value
Assets
Risk Management Assets	215.9	119.3
Liabilities
Risk Management Liabilities	$ 161.0	$ 159.9