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Summary of Significant Accounting Policies - MEC - Inventory (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Inventory [Line Items]    
Inventory, Raw Materials and Supplies, Gross $ 523 $ 529
Replacement cost of inventory 27 8
MidAmerican Energy Company [Member]    
Inventory [Line Items]    
Inventory, Raw Materials and Supplies, Gross 99 105
Public utility inventory, coal 137 102
Public utility inventory - natural gas in storage 24 27
Replacement cost of inventory $ 27 $ 8