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Employee Benefit Plans - MEC - Asset Allocations (Details) - MidAmerican Energy Company [Member]
12 Months Ended
Dec. 31, 2017
Minimum [Member] | Pension Plan [Member] | Debt Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .20 [1]
Minimum [Member] | Pension Plan [Member] | Equity Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .6 [1]
Minimum [Member] | Pension Plan [Member] | Real Estate Funds [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .02
Minimum [Member] | Pension Plan [Member] | Other Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .00
Minimum [Member] | Other Postretirement Benefits Plan [Member] | Debt Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .25 [1]
Minimum [Member] | Other Postretirement Benefits Plan [Member] | Equity Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .5 [1]
Minimum [Member] | Other Postretirement Benefits Plan [Member] | Real Estate Funds [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .00
Minimum [Member] | Other Postretirement Benefits Plan [Member] | Other Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .00
Maximum [Member] | Pension Plan [Member] | Debt Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .4 [1]
Maximum [Member] | Pension Plan [Member] | Equity Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .8 [1]
Maximum [Member] | Pension Plan [Member] | Real Estate Funds [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .08
Maximum [Member] | Pension Plan [Member] | Other Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .05
Maximum [Member] | Other Postretirement Benefits Plan [Member] | Debt Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .45 [1]
Maximum [Member] | Other Postretirement Benefits Plan [Member] | Equity Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .80 [1]
Maximum [Member] | Other Postretirement Benefits Plan [Member] | Real Estate Funds [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage 0
Maximum [Member] | Other Postretirement Benefits Plan [Member] | Other Securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Defined Benefit Plan, Target Allocation Percentage .05
[1] (1)For purposes of target allocation percentages and consistent with the plans' investment policy, investment funds are allocated based on the underlying investments in debt and equity securities.