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Income Taxes (LLC) Reconciliation of Effective Income Tax Rate (Details) (MidAmerican Funding, LLC and Subsidiaries [Domain], USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]      
Federal statutory income tax rate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Income tax credits (61.00%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits (75.00%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits (60.00%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits
State income tax, net of federal income tax benefit (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes (3.00%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes (12.00%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Income tax method changes 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes (6.00%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes
Effects of ratemaking (9.00%)mec_EffectiveIncomeTaxRateReconciliationRegulatoryDifferences (3.00%)mec_EffectiveIncomeTaxRateReconciliationRegulatoryDifferences (1.00%)mec_EffectiveIncomeTaxRateReconciliationRegulatoryDifferences
Other, net (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments (2.00%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments (2.00%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Effective income tax rate (37.00%)us-gaap_EffectiveIncomeTaxRateContinuingOperations (48.00%)us-gaap_EffectiveIncomeTaxRateContinuingOperations (46.00%)us-gaap_EffectiveIncomeTaxRateContinuingOperations
Production Tax Credit Carryforwards [Abstract]      
Years eligible for renewable energy production tax credit 10 years    
Repairs deduction [Member]
     
Income tax method change [Abstract]      
Income tax benefits from tax method change   16us-gaap_IncomeTaxReconciliationPriorYearIncomeTaxes
/ mec_IncometaxmethodchangeAxis
= mec_RepairsDeductionMember
/ dei_LegalEntityAxis
= mec_MidamericanFundingLlcAndSubsidiariesDomain