SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AFUDC (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
AFUDC
Percentage of retail jurisdictional construction work in progress expenditures subject to AFUDC calculation	50.00%
Allowance for equity funds used during construction	$ 11.0	$ 9.9	$ 2.6
Allowance for borrowed funds used during construction	$ 4.6	$ 3.8	$ 0.9
Retail
AFUDC
Average AFUDC rate (as a percent)	8.08%
Wholesale
AFUDC
Average AFUDC rate (as a percent)	6.99%

The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount capitalized of allowance for funds used during construction.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

+ References

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- Details

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- Definition

Represents the percentage of retail jurisdictional construction work in progress expenditures subject to the AFUDC calculation.

+ References

No definition available.

+ Details

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- Details

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