Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
New 401k Contribution for new hires				6.00%wec_New401kContributionfornewhires
Pension Plans [Member]
Change in Benefit Obligation
Benefit Obligation at January 1	$ 1,410.2	$ 1,508.5
Service cost	10.1	14.6	21.7
Interest cost	68.1	60.4	65.5
Participants' contributions	0	0
Plan amendments	0	(1.0)
Actuarial loss (gain)	120.4	(81.9)
Gross benefits paid	(103.3)	(90.4)
Benefit Obligation at December 31	1,505.5	1,410.2	1,508.5
OPEB [Member]
Change in Benefit Obligation
Benefit Obligation at January 1	362.7	381.2
Service cost	8.5	10.0	10.3
Interest cost	17.8	15.6	20.3
Participants' contributions	9.1	8.9
Plan amendments	(4.6)	0
Actuarial loss (gain)	29.4	(27.7)
Gross benefits paid	(26.4)	(26.3)
Federal subsidy on benefits paid	1.2	1.0
Benefit Obligation at December 31	$ 397.7	$ 362.7	$ 381.2

Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Gain or Loss

-URI http://asc.fasb.org/extlink&oid=6514294

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

-Publisher FASB

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- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

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-Glossary Projected Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6522206

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Postretirement Benefits

-URI http://asc.fasb.org/extlink&oid=6521376

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

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-Topic 715

-SubTopic 60

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-Publisher FASB

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- Definition

The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Plan Amendment

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

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-Glossary Service Cost (Component of Net Periodic Pension Cost)

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Federal subsidy on benefits paid.

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New 401k Contribution for new hires

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