FAIR VALUE (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Risk Management Assets	$ 243.9	$ 190.7
Liabilities
Risk Management Liabilities	262.4	240.3
Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	87.6	70.3
Investment in Exchange Traded Funds	12.7	11.8
Liabilities
Risk Management Liabilities	99.2	73.7
Contingent Consideration	0
Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	112.4	100.8
Investment in Exchange Traded Funds	0	0
Liabilities
Risk Management Liabilities	132.7	142.1
Contingent Consideration	0
Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	43.9	19.6
Investment in Exchange Traded Funds	0	0
Liabilities
Risk Management Liabilities	30.5	24.5
Contingent Consideration	7.7
Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	243.9	190.7
Investment in Exchange Traded Funds	12.7	11.8
Liabilities
Risk Management Liabilities	262.4	240.3
Contingent Consideration	7.7
Utility Segments | Natural gas contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0.5	0.3
Liabilities
Risk Management Liabilities	0.9	1.1
Utility Segments | Natural gas contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	2.1	3.1
Liabilities
Risk Management Liabilities	6.6	14.1
Utility Segments | Natural gas contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | Natural gas contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	2.6	3.4
Liabilities
Risk Management Liabilities	7.5	15.2
Utility Segments | FTRs | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | FTRs | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0	0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | FTRs | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	4.5	2.1
Liabilities
Risk Management Liabilities	0.6	0.1
Utility Segments | FTRs | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	4.5	2.1
Liabilities
Risk Management Liabilities	0.6	0.1
Utility Segments | Petroleum product contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0.2
Liabilities
Risk Management Liabilities	0.1
Utility Segments | Petroleum product contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0
Liabilities
Risk Management Liabilities	0
Utility Segments | Petroleum product contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0
Liabilities
Risk Management Liabilities	0
Utility Segments | Petroleum product contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0.2
Liabilities
Risk Management Liabilities	0.1
Utility Segments | Coal contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | Coal contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets		0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | Coal contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0	2.5
Liabilities
Risk Management Liabilities	2.3	9.0
Utility Segments | Coal contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets		2.5
Liabilities
Risk Management Liabilities	2.3	9.0
Nonregulated Segments | Level 3 | Fair value measurements on a recurring basis
Liabilities
Contingent Consideration	7.7
Nonregulated Segments | Natural gas contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	9.8	21.4
Liabilities
Risk Management Liabilities	18.1	17.7
Nonregulated Segments | Natural gas contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	56.9	36.4
Liabilities
Risk Management Liabilities	36.2	36.9
Nonregulated Segments | Natural gas contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	23.7	5.4
Liabilities
Risk Management Liabilities	16.0	1.5
Nonregulated Segments | Natural gas contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	90.4	63.2
Liabilities
Risk Management Liabilities	70.3	56.1
Nonregulated Segments | Electric contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	77.3	48.4
Liabilities
Risk Management Liabilities	80.1	54.9
Nonregulated Segments | Electric contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	53.4	61.3
Liabilities
Risk Management Liabilities	89.9	91.1
Nonregulated Segments | Electric contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	15.7	9.6
Liabilities
Risk Management Liabilities	11.6	13.9
Nonregulated Segments | Electric contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	146.4	119.3
Liabilities
Risk Management Liabilities	$ 181.6	$ 159.9