Derivative Financial Instruments (Schedule Of Derivative Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - current	$ 43	$ 14
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - noncurrent	7	0
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - current	17	77
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - noncurrent	12	7
Derivatives not designated as hedging instruments
Derivative [Line Items]
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives	50	14
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives	29	84
Derivatives not designated as hedging instruments | Commodity price derivatives | Derivatives - current
Derivative [Line Items]
Asset Derivatives, Fair Value	50	33
Liability Derivatives, Fair Value	29	102
Gross Amounts Offset in the Consolidated Balance Sheet, Assets Derivatives	(12)	(25)
Gross Amounts Offset in the Consolidated Balance Sheet. Liabilities Derivatives	(12)	(25)
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - current	38	8
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - current	17	77
Derivatives not designated as hedging instruments | Commodity price derivatives | Derivatives - noncurrent
Derivative [Line Items]
Asset Derivatives, Fair Value	10
Liability Derivatives, Fair Value	15	7
Gross Amounts Offset in the Consolidated Balance Sheet, Assets Derivatives	(3)
Gross Amounts Offset in the Consolidated Balance Sheet. Liabilities Derivatives	(3)	0
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - noncurrent	7
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - noncurrent	12	7
Derivatives not designated as hedging instruments | Interest rate derivatives | Derivatives - current
Derivative [Line Items]
Asset Derivatives, Fair Value	5	6
Gross Amounts Offset in the Consolidated Balance Sheet, Assets Derivatives	0	0
Net Fair Value Presented in the Consolidated Balance Sheet, Asset Derivatives - current	$ 5	$ 6