Commodity And Other Derivative Contractual Assets And Liabilities (Financial Statement Effects of Derivatives) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	$ 1,132	$ 2,049
Derivative liabilities, Fair Value, Gross Liability	(1,376)	(2,450)
Derivative, Fair Value, Net	(244)	(401)
Current assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets And Liability, Fair Value, Gross Assets	973	1,463
Noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets And Liability, Fair Value, Gross Assets	159	586
Current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets And Liability, Fair Value, Gross Liability	(594)	(894)
Noncurrent liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets And Liability, Fair Value, Gross Liability	(782)	(1,556)
Commodity contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	1,131	2,047
Derivative liabilities, Fair Value, Gross Liability	(209)	(383)
Derivative asset, Fair Value, Net	1,129	2,047
Derivative liabilities, Fair Value, Net	(207)	(383)
Commodity contracts [Member] | Current assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	972	1,461
Derivative liabilities, Fair Value, Gross Asset	0	0
Commodity contracts [Member] | Noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	159	586
Derivative liabilities, Fair Value, Gross Asset	0	0
Commodity contracts [Member] | Current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Liability	(2)	0
Derivative liabilities, Fair Value, Gross Liability	(204)	(366)
Commodity contracts [Member] | Noncurrent liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Liability	0	0
Derivative liabilities, Fair Value, Gross Liability	(3)	(17)
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	1	2
Derivative liabilities, Fair Value, Gross Liability	(1,167)	(2,067)
Derivative asset, Fair Value, Net	1	2
Derivative liabilities, Fair Value, Net	(1,167)	(2,067)
Interest rate swaps [Member] | Current assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	1	2
Derivative liabilities, Fair Value, Gross Asset	0	0
Interest rate swaps [Member] | Noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Asset	0	0
Derivative liabilities, Fair Value, Gross Asset	0	0
Interest rate swaps [Member] | Current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Liability	0	0
Derivative liabilities, Fair Value, Gross Liability	(388)	(528)
Interest rate swaps [Member] | Noncurrent liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, Fair Value, Gross Liability	0	0
Derivative liabilities, Fair Value, Gross Liability	$ (779)	$ (1,539)