Fair Value Measurements - Assets and liabilities measured on a recurring basis (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets
Derivative asset	$ 41.6	$ 9.9
Liabilities
Derivative liability	2.4	59.0
Fair value measurements on a recurring basis
Assets
Derivative asset	41.6	9.9
Investment in exchange-traded funds	103.9	39.8
Liabilities
Derivative liability	2.4	59.0
Fair value measurements on a recurring basis \| Level 1
Assets
Derivative asset	10.3	2.8
Investment in exchange-traded funds	103.9	39.8
Liabilities
Derivative liability	0.3	21.4
Fair value measurements on a recurring basis \| Level 2
Assets
Derivative asset	26.2	3.5
Investment in exchange-traded funds	0.0	0.0
Liabilities
Derivative liability	2.1	37.6
Fair value measurements on a recurring basis \| Level 3
Assets
Derivative asset	5.1	3.6
Investment in exchange-traded funds	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Fair value measurements on a recurring basis \| Natural gas contracts
Assets
Derivative asset	34.3	3.1
Liabilities
Derivative liability	0.4	41.8
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 1
Assets
Derivative asset	10.1	1.6
Liabilities
Derivative liability	0.2	16.5
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 2
Assets
Derivative asset	24.2	1.5
Liabilities
Derivative liability	0.2	25.3
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 3
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Fair value measurements on a recurring basis \| Petroleum products contracts
Assets
Derivative asset	0.2	1.2
Liabilities
Derivative liability	0.1	4.9
Fair value measurements on a recurring basis \| Petroleum products contracts \| Level 1
Assets
Derivative asset	0.2	1.2
Liabilities
Derivative liability	0.1	4.9
Fair value measurements on a recurring basis \| Petroleum products contracts \| Level 2
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Fair value measurements on a recurring basis \| Petroleum products contracts \| Level 3
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Fair value measurements on a recurring basis \| FTRs
Assets
Derivative asset	5.1	3.6
Fair value measurements on a recurring basis \| FTRs \| Level 1
Assets
Derivative asset	0.0	0.0
Fair value measurements on a recurring basis \| FTRs \| Level 2
Assets
Derivative asset	0.0	0.0
Fair value measurements on a recurring basis \| FTRs \| Level 3
Assets
Derivative asset	5.1	3.6
Fair value measurements on a recurring basis \| Coal contracts
Assets
Derivative asset	2.0	2.0
Liabilities
Derivative liability	1.9	12.3
Fair value measurements on a recurring basis \| Coal contracts \| Level 1
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	0.0	0.0
Fair value measurements on a recurring basis \| Coal contracts \| Level 2
Assets
Derivative asset	2.0	2.0
Liabilities
Derivative liability	1.9	12.3
Fair value measurements on a recurring basis \| Coal contracts \| Level 3
Assets
Derivative asset	0.0	0.0
Liabilities
Derivative liability	$ 0.0	$ 0.0

No definition available.

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

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

+ References

+ Details

Name:	us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26626-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=wec_CommodityContractNaturalGasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=wec_CommodityContractPetroleumProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=wec_CommodityContractFinancialTransmissionRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CoalContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: