Derivative and Financial Instruments - Commodity Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative assets	$ 3,593	$ 4,500
Other assets [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative assets	162	157
Other accruals [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative liabilities	3,590	4,426
Other liabilities and deferred credits [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative liabilities	$ 157	$ 144