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Risk Management and Hedging Activities - MEC - Collateral and Contingent Features (Details) - Commodity Contract [Member] - USD ($)
$ in Millions
Dec. 31, 2015
Dec. 31, 2014
Derivative [Line Items]    
Derivative, Net Liability Position, Aggregate Fair Value $ 288 $ 243
Additional Collateral, Aggregate Fair Value 198 182
Collateral Already Posted, Aggregate Fair Value 75 28
MidAmerican Energy Company [Member]    
Derivative [Line Items]    
Derivative, Net Liability Position, Aggregate Fair Value 66 52
Additional Collateral, Aggregate Fair Value 55 36
Collateral Already Posted, Aggregate Fair Value $ 0 $ 0