Materials, Supplies and Inventory (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Inventory [Line Items]
Fossil Fuel	$ 182,400,000	$ 125,600,000
Materials and Supplies	249,700,000	150,200,000
Natural Gas in Storage	130,400,000	124,800,000
Total	562,500,000	$ 400,600,000
PGL
Inventory [Line Items]
Temporary LIFO liquidation debit	21.0
NSG
Inventory [Line Items]
Temporary LIFO liquidation credit	$ 5.2

Carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies relating to a source of usable power held for future sale or future use in manufacturing or production process.

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- Definition

Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale.

+ References

+ Details

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- Definition

Carrying amount as of the balance sheet date of other types of fuel derived from living matter of a previous geologic time, not otherwise itemized.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Aggregated amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed. This amount is net of valuation reserves and adjustments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a)(4),(5))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.BB)

-URI http://asc.fasb.org/extlink&oid=27011343&loc=d3e100047-122729

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section BB

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- Definition

Represents the difference between current projected replacement cost and the LIFO cost for quantities of natural gas temporarily withdrawn from storage.

+ References

No definition available.

+ Details

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- Definition

Represents the difference between current projected replacement cost and the LIFO cost for quantities of natural gas temporarily withdrawn from storage.

+ References

No definition available.

+ Details

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Namespace Prefix:	wec_
Data Type:	xbrli:monetaryItemType
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