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Debt (Pollution Control and Industrial Revenue Bonds) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Debt Instrument [Line Items]      
Refinancing expense $ 2 $ 0  
Refunding loan for pollution control and industrial revenue bonds [Member]      
Debt Instrument [Line Items]      
Refunding revenue and pollution control debt 170   $ 0
Deferred Finance Costs, Gross (2)    
Pollution Control and Industrial Revenue Bonds [Member]      
Debt Instrument [Line Items]      
Refinancing expense 2    
Refunding revenue and pollution control debt $ 0   $ 169