FAIR VALUE - TRANSFERS BETWEEN LEVELS (Details) (Fair value measurements on a recurring basis, Nonregulated segments, USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Natural gas contracts
Transfers between the levels of the fair value hierarchy
Transfers into Level 2 from Level 1	$ 0	$ 0
Transfers into Level 3 from Level 1	0	0
Transfers into Level 1 from Level 2	0	0
Transfers into Level 3 from Level 2	0.9	0.2
Transfers into Level 1 from Level 3	0	0
Transfers into Level 2 from Level 3	0.1	0
Electric contracts
Transfers between the levels of the fair value hierarchy
Transfers into Level 2 from Level 1	0	0
Transfers into Level 3 from Level 1	0	0
Transfers into Level 1 from Level 2	0	0
Transfers into Level 3 from Level 2	2.6	0
Transfers into Level 1 from Level 3	0	0
Transfers into Level 2 from Level 3	$ 4.4	$ 5.5

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The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 3.

+ References

No definition available.

+ Details

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- Definition

The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 3.

+ References

No definition available.

+ Details

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- Definition

The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 3 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

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- Definition

The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 3 of the fair value hierarchy into Level 2.

+ References

No definition available.

+ Details

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- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

+ Details

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- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

+ Details

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