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Derivative and Financial Instruments - Credit Risk (Details Textual) - USD ($)
6 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Aggregate fair value of all derivative instruments in a liability position $ 73,000,000 $ 62,000,000
Collateral was posted for derivative instruments in a liability position 0  
In event of downgrade below investment grade [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Additional collateral, either in the form of cash or letters of credit $ 71,000,000  
Financial instruments [Member] | Maximum [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Terms of financial instruments and trade receivables 90 days  
Trade receivables [Member] | Maximum [Member]    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Terms of financial instruments and trade receivables 30 days