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Risk Management and Hedging Activities - MEC - Collateral and Contingent Features (Details) - Commodity derivative [Member] - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Derivative [Line Items]    
Collateral already posted, aggregate fair value $ 73 $ 75
Derivative, net liability position, aggregate fair value 227 288
Additional collateral, aggregate fair value 139 198
MidAmerican Energy Company [Member]    
Derivative [Line Items]    
Collateral already posted, aggregate fair value 0 0
Derivative, net liability position, aggregate fair value 7 66
Additional collateral, aggregate fair value $ 3 $ 55