Derivative Financial Instruments (Schedule Of Derivative Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - current	$ 7	$ 11
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - current	333	232
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - noncurrent	54	23
Derivatives not designated as hedging instruments
Derivative [Line Items]
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives	7	11
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives	387	255
Derivatives not designated as hedging instruments | Commodity price derivatives | Derivatives - current
Derivative [Line Items]
Asset Derivatives, Fair Value	14	13
Gross Amounts Offset in the Consolidated Balance Sheet, Assets Derivatives	(7)	(2)
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - current	7	11
Liability Derivatives, Fair Value	340	234
Gross Amounts Offset in the Consolidated Balance Sheet. Liabilities Derivatives	(7)	(2)
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - current	333	232
Derivatives not designated as hedging instruments | Commodity price derivatives | Derivatives - noncurrent
Derivative [Line Items]
Asset Derivatives, Fair Value	8	3
Gross Amounts Offset in the Consolidated Balance Sheet, Assets Derivatives	(8)	(3)
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - noncurrent	0	0
Liability Derivatives, Fair Value	62	26
Gross Amounts Offset in the Consolidated Balance Sheet. Liabilities Derivatives	(8)	(3)
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - noncurrent	$ 54	$ 23