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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.D)
-URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030

+ Details

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

- 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

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Firm capacity, in megawatts, from a purchased power agreement accounted for as a finance lease.

+ References

No definition available.

+ Details

Name:	wec_FirmCapacityFromFinanceLeasePurchasedPowerAgreement
Namespace Prefix:	wec_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum energy requirements, in megawatts, over the remaining term of a purchased power agreement accounted for as a finance lease.

+ References

No definition available.

+ Details

Name:	wec_MinimumEnergyRequirementsFinanceLeasePurchasedPowerAgreement
Namespace Prefix:	wec_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

The remaining term, in years, of a purchased power agreement accounted for as a capital lease.

+ References

No definition available.

+ Details

Name:	wec_RemainingTermOfFinanceLeasePurchasedPowerAgreement
Namespace Prefix:	wec_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the residual guarantee associated with a purchased power agreement accounted for as a finance lease.

+ References

No definition available.

+ Details

Name:	wec_ResidualGuaranteeFinanceLeasePurchasedPowerAgreement
Namespace Prefix:	wec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=wec_AmericanTransmissionCompanyLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=wec_ATCHoldCoLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=wec_PurchasedPowerAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

VARIABLE INTEREST ENTITIES (Details) $ in Millions	9 Months Ended
VARIABLE INTEREST ENTITIES (Details) $ in Millions	Sep. 30, 2019 USD ($) MW	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Variable interest entities
Equity investment	$ 1,720.4	$ 1,696.5	$ 1,665.3	$ 1,613.7	$ 1,596.6	$ 1,553.4
ATC
Variable interest entities
Ownership interest (as a percent)	60.00%
Equity investment	$ 1,679.8		1,625.3
ATC Holdco
Variable interest entities
Ownership interest (as a percent)	75.00%
Equity investment	$ 40.6		$ 40.0
Purchased power agreement
Variable interest entities
Firm capacity from purchased power agreement (in megawatts) \| MW	236
Minimum energy requirements over remaining term of purchased power agreement (in megawatts) \| MW	0
Remaining term of purchased power agreement (in years)	3 years
Residual guarantee associated with purchased power agreement	$ 0.0
Required payments over remaining term of purchased power agreement	$ 24.4