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Debt (Pollution Control and Industrial Revenue Bonds) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2016
Mar. 31, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Debt Instrument [Line Items]          
Refinancing expense $ 0   $ 0 $ 2 $ 0
Refunding loan for pollution control and industrial revenue bonds [Member]          
Debt Instrument [Line Items]          
Deferred Finance Costs, Gross   $ 2      
Pollution Control and Industrial Revenue Bonds [Member]          
Debt Instrument [Line Items]          
Refinancing expense   $ 2