Fair Value Measurements (Details 3-Reported)	Dec. 31, 2017 USD ($)	May 31, 2017	Jun. 30, 2018 USD ($)
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Assets, Fair Value Disclosure	$ 762,000,000		$ 48,000,000
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Other noncurrent financial assets	135,000,000		85,000,000
Total financial assets	897,000,000		133,000,000
Financial liabilities
Other current financial liabilities	32,000,000		32,000,000
Long-term debt, including current portion	5,976,000,000		5,791,000,000
Deferred credits and other financial liabilities	110,000,000		100,000,000
Financial Liabilities Fair Value Disclosure	6,118,000,000		5,923,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Assets, Fair Value Disclosure	761,000,000		48,000,000
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Other noncurrent financial assets	137,000,000		89,000,000
Total financial assets	898,000,000		137,000,000
Financial liabilities
Other current financial liabilities	43,000,000		44,000,000
Long-term debt, including current portion	5,526,000,000		5,528,000,000
Deferred credits and other financial liabilities	103,000,000		97,000,000
Financial Liabilities Fair Value Disclosure	$ 5,672,000,000		$ 5,669,000,000
Oil Sands Mining Segment [Member] | Discontinued Operations, Disposed of by Sale [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of notes receivable	2	2