Short-Term Debt and Lines of Credit - Credit Facilities (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) extension	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 2,800.0
Letters of credit issued inside credit facilities	7.9
Commercial paper	1,444.6	$ 860.2
Available capacity under existing agreements	1,347.5
WEC Energy Group
Line of Credit Facility [Line Items]
Commercial paper	494.8	$ 321.8
WEC Energy Group \| Credit facility maturing October 2022
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 1,200.0
Number of extensions available on a credit facility \| extension	2
Length of credit facility extension	1 year
WE \| Credit facility maturing October 2022
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 500.0
Number of extensions available on a credit facility \| extension	2
Length of credit facility extension	1 year
WPS \| Credit facility maturing December 2020
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 400.0
Number of extensions available on a credit facility \| extension	2
Length of credit facility extension	1 year
WG \| Credit facility maturing October 2022
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 350.0
Number of extensions available on a credit facility \| extension	2
Length of credit facility extension	1 year
PGL \| Credit facility maturing October 2022
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 350.0
Number of extensions available on a credit facility \| extension	2
Length of credit facility extension	1 year
Commercial paper
Line of Credit Facility [Line Items]
Commercial paper	$ 1,444.6

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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(19)(a)(3))
-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 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13)(2))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- 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

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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- Definition

Length of time a credit facility can be extended.

+ References

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- Definition

Number of extensions available on credit facility

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