COMMON EQUITY - DIVIDEND RESTRICTIONS (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Dividend Payment Restrictions
Maximum debt to capitalization ratio required to be maintained (as a percent)	65.00%teg_MaximumDebttoCapitalizationRatio
Total restricted net assets for consolidated subsidiaries	$ 1,872.6
Equity in undistributed earnings of 50% or less owned investees accounted for by the equity method	$ 158.1
Dividends per common share declared (in dollars per share)	$ 0.68	$ 0.68
Maximum
Dividend Payment Restrictions
Equity method investment, ownership interest (as a percent)	50.00%
Cumulative period of interest payment deferral on Junior Subordinated Notes	10 years
Dividends per common share declared (in dollars per share)	$ 0.68
Minimum
Dividend Payment Restrictions
Number of periods for which interest payments can be deferred on Junior Subordinated Notes	1
PGL
Dividend Payment Restrictions
Maximum debt to capitalization ratio required to be maintained (as a percent)	65.00%
WPS
Dividend Payment Restrictions
Maximum debt to capitalization ratio required to be maintained (as a percent)	65.00%
WPS \| Maximum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Percentage of previous period's dividend as restriction on current period dividends	103.00%
WPS \| Minimum
Dividend Payment Restrictions
Percentage of common stockholders' equity to total capitalization required to be maintained	25.00%
WPS \| Minimum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Common equity ratio required to be maintained (as a percent)	51.00%

Amount of restricted net assets of consolidated subsidiaries as of the end of the most recently completed period.

No definition available.

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- Definition

Represents the common equity ratio which is required to be maintained.

+ References

No definition available.

+ Details

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- Definition

Represents the number of periods for which interest payments on junior subordinated notes can be deferred.

+ References

No definition available.

+ Details

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- Definition

Represents the number of consecutive years for which interest payments on junior subordinated notes can be deferred.

+ References

No definition available.

+ Details

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- Details

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- Definition

Represents the percentage of common stockholders equity to total capitalization for dividend payment restrictions.

+ References

No definition available.

+ Details

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- Definition

Represents the maximum debt to capitalization ratio.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of previous period's dividend as restriction on current period's dividends.

+ References

No definition available.

+ Details

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- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

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- Definition

Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50% or less owned persons accounted for by the equity method (equity method investees).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 20

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6462270&loc=d3e57205-112772

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