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Common Equity (Details 2) (USD $)
 12 Months Ended
Dec. 31, 2014
Stock options outstanding  
Options Outstanding, Number, Total 6,770,194us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Options Outstanding, Weighted-Average Exercise Price $ 29.99us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Options Outstanding, Weighted-Average Remaining Contractual Life (Years) 5 years 8 months
Options Exercisable, Number, Total 3,890,339us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Options Exercisable, Weighted-Average Exercise Price $ 24.10us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
Options Exercisable, Weighted-Average Remaining Contractual Life (Years) 3 years 11 months
Exercise Price, Range One [Member]  
Stock options outstanding  
Options Outstanding, Number, Total 1,498,071us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Options Outstanding, Weighted-Average Exercise Price $ 20.86us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Options Outstanding, Weighted-Average Remaining Contractual Life (Years) 3 years 6 months
Options Exercisable, Number, Total 1,498,071us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Options Exercisable, Weighted-Average Exercise Price $ 20.86us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Options Exercisable, Weighted-Average Remaining Contractual Life (Years) 3 years 6 months
Exercise Price, Range One [Member] | Maximum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 21.11us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Exercise Price, Range One [Member] | Minimum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 17.10us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeOneMember
Exercise Price, Range Two [Member]  
Stock options outstanding  
Options Outstanding, Number, Total 2,153,513us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Options Outstanding, Weighted-Average Exercise Price $ 25.06us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Options Outstanding, Weighted-Average Remaining Contractual Life (Years) 3 years 8 months
Options Exercisable, Number, Total 2,153,513us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Options Exercisable, Weighted-Average Exercise Price $ 25.06us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Options Exercisable, Weighted-Average Remaining Contractual Life (Years) 3 years 8 months
Exercise Price, Range Two [Member] | Maximum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 29.35us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Exercise Price, Range Two [Member] | Minimum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 23.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeTwoMember
Exercise Price, Range Three [Member]  
Stock options outstanding  
Options Outstanding, Number, Total 3,118,610us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember
Options Outstanding, Weighted-Average Exercise Price $ 37.79us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember
Options Outstanding, Weighted-Average Remaining Contractual Life (Years) 8 years 0 months
Options Exercisable, Number, Total 238,755us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember
Options Exercisable, Weighted-Average Exercise Price $ 35.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember
Options Exercisable, Weighted-Average Remaining Contractual Life (Years) 7 years 5 months
Exercise Price, Range Three [Member] | Maximum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 41.03us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember
Exercise Price, Range Three [Member] | Minimum [Member]  
Stock options outstanding  
Options Outstanding, Weighted-Average Exercise Price $ 34.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= wec_ExercisePriceRangeThreeMember