Derivative and Financial Instruments (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate fair value of all derivative instruments in a liability position	$ 61	$ 55
Collateral was posted for derivative instruments in a liability position	0	$ 0
In event of lowered credit rating [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Additional collateral, either in the form of cash or letters of credit	$ 61
Financial instruments [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Terms of financial instruments and trade receivables	90 days
Credit Derivative, Recourse Provisions	Certain of our derivative instruments contain provisions that require us to post collateral if the derivative exposure exceeds a threshold amount. We have contracts with fixed threshold amounts and other contracts with variable threshold amounts that are contingent on our credit rating. The variable threshold amounts typically decline for lower credit ratings, while both the variable and fixed threshold amounts typically revert to zero if we fall below investment grade. Cash is the primary collateral in all contracts; however, many also permit us to post letters of credit as collateral, such as transactions administered through the New York Mercantile Exchange.
Trade receivables [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Terms of financial instruments and trade receivables	30 days