FAIR VALUE (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Risk Management Assets	$ 213.0	$ 190.7
Liabilities
Risk Management Liabilities	217.1	240.3
Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	80.9	70.3
Investment in Exchange Traded Funds	13.4	11.8
Liabilities
Risk Management Liabilities	92.6	73.7
Contingent Consideration	0
Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	93.1	100.8
Investment in Exchange Traded Funds	0	0
Liabilities
Risk Management Liabilities	101.6	142.1
Contingent Consideration	0
Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	39.0	19.6
Investment in Exchange Traded Funds	0	0
Liabilities
Risk Management Liabilities	22.9	24.5
Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	213.0	190.7
Investment in Exchange Traded Funds	13.4	11.8
Liabilities
Risk Management Liabilities	217.1	240.3
Contingent Consideration	7.7
Utility Segments | Natural gas contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0.9	0.3
Liabilities
Risk Management Liabilities	0.8	1.1
Utility Segments | Natural gas contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	1.8	3.1
Liabilities
Risk Management Liabilities	5.2	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	2.7	3.4
Liabilities
Risk Management Liabilities	6.0	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	3.4	2.1
Liabilities
Risk Management Liabilities	0.4	0.1
Utility Segments | FTRs | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	3.4	2.1
Liabilities
Risk Management Liabilities	0.4	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	0.2
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	0.2
Utility Segments | Coal contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	0	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	0
Liabilities
Risk Management Liabilities	0	0
Utility Segments | Coal contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	1.5	2.5
Liabilities
Risk Management Liabilities	2.7	9.0
Utility Segments | Coal contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	1.5	2.5
Liabilities
Risk Management Liabilities	2.7	9.0
Nonregulated Segments | Natural gas contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	9.9	21.4
Liabilities
Risk Management Liabilities	16.0	17.7
Nonregulated Segments | Natural gas contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	42.3	36.4
Liabilities
Risk Management Liabilities	26.5	36.9
Nonregulated Segments | Natural gas contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	21.3	5.4
Liabilities
Risk Management Liabilities	9.7	1.5
Nonregulated Segments | Natural gas contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	73.5	63.2
Liabilities
Risk Management Liabilities	52.2	56.1
Nonregulated Segments | Electric contracts | Level 1 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	70.1	48.4
Liabilities
Risk Management Liabilities	75.6	54.9
Nonregulated Segments | Electric contracts | Level 2 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	49.0	61.3
Liabilities
Risk Management Liabilities	69.9	91.1
Nonregulated Segments | Electric contracts | Level 3 | Fair value measurements on a recurring basis
Assets
Risk Management Assets	12.8	9.6
Liabilities
Risk Management Liabilities	10.1	13.9
Nonregulated Segments | Electric contracts | Total, Fair value | Fair value measurements on a recurring basis
Assets
Risk Management Assets	131.9	119.3
Liabilities
Risk Management Liabilities	$ 155.6	$ 159.9