Derivative Instruments, Open Positions (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Derivative [Line Items]
Maturity of foreign currency derivatives	January 25, 2012
Forward contract to purchase Canadian dollars	$ 64
Fair Value Hedges [Member] | Forwards [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	0
Fair Value Hedges [Member] | Futures [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	0
Fair Value Hedges [Member] | Swaps [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	0
Mark-to-Market Derivatives [Member] | Forwards [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	(1,026,000)
Mark-to-Market Derivatives [Member] | Futures [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	(3,008,000)
Mark-to-Market Derivatives [Member] | Swaps [Member] | 2012 [Member]
Derivative [Line Items]
Long (Short) Contract Volumes (in thousands of barrels)	(321,000)