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Derivative Instruments (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
MMBTU
Dec. 31, 2016
USD ($)
MMBTU
Natural Gas Hedge [Member] | Prepaid and Other Assets [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Fair value of derivative instruments in hedges $ 1 $ 3
Natural Gas Hedge [Member] | Accumulated Other Comprehensive Loss [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Offset amount recognized against derivative asset $ 2  
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Natural Gas Commodity Price Contracts [Member] | Forward Contracts [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative contracts, maturity date Dec. 31, 2017  
Aggregate notional volume of outstanding natural gas commodity forward contracts | MMBTU 3.8 4.8