Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets:
Net Fair Value Presented in the Consolidated Balance Sheet, current	$ 5	$ 32
Derivative Asset, Noncurrent	3	21
Derivative Liability [Abstract]
Net Fair Value Presented in the Consolidated Balance Sheet, current	234	12
Net Fair Value Presented in the Consolidated Balance Sheet, noncurrent	66	8
Derivatives not designated as hedging instruments
Assets:
Net Fair Value Presented in the Consolidated Balance Sheet, total
Derivative Liability [Abstract]
Net Fair Value Presented in the Consolidated Balance Sheet, total
Derivatives - current \| Derivatives not designated as hedging instruments \| Commodity price derivatives
Assets:
Fair Value	5	32
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Fair Value Presented in the Consolidated Balance Sheet, current	5	32
Derivative Liability [Abstract]
Fair Value	(198)	(12)
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Fair Value Presented in the Consolidated Balance Sheet, current	198	12
Derivatives - current \| Derivatives not designated as hedging instruments \| Marketing derivatives
Derivative Liability [Abstract]
Fair Value	(36)
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Fair Value Presented in the Consolidated Balance Sheet, current	36
Derivatives - noncurrent \| Derivatives not designated as hedging instruments \| Commodity price derivatives
Assets:
Fair Value	3
Gross Amounts Offset in the Consolidated Balance Sheet	0
Derivative Asset, Noncurrent	3
Derivative Liability [Abstract]
Fair Value	(11)	(8)
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Fair Value Presented in the Consolidated Balance Sheet, noncurrent	(11)	8
Derivatives - noncurrent \| Derivatives not designated as hedging instruments \| Contingent Consideration [Member]
Assets:
Fair Value		91
Gross Amounts Offset in the Consolidated Balance Sheet		0
Derivative Asset, Noncurrent		91
Derivatives - noncurrent \| Derivatives not designated as hedging instruments \| Marketing derivatives
Assets:
Fair Value		21
Gross Amounts Offset in the Consolidated Balance Sheet		0
Derivative Asset, Noncurrent		$ 21
Derivative Liability [Abstract]
Fair Value	(55)
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Fair Value Presented in the Consolidated Balance Sheet, noncurrent	$ (55)

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