Commitments and Contingencies, Purchase Obligations and Other Commitments (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Purchase Obligations and Other Commitments [Line Items]
Crude oil purchase commitment terms	7
Purchase obligation term past 2016	9
Payments under take-or-pay contracts	$ 433	$ 338	$ 300
Crude oil commitments [Member]
Purchase Obligations and Other Commitments [Line Items]
Minimum payment in 2012	5,800
Minimum payment in 2013	2,100
Minimum payment in 2014	2,800
Minimum payment in 2015	2,100
Minimum payment in 2016	1,600
Minimum payment after 2016	1,900
Price per barrel purchase commitment low range	$ 71
Price per barrel purchase commitment high range	$ 106
Capital spending commitments [Member]
Purchase Obligations and Other Commitments [Line Items]
Minimum payment in 2012	83
Take or pay commitments [Member]
Purchase Obligations and Other Commitments [Line Items]
Minimum payment in 2012	311
Minimum payment in 2013	144
Minimum payment in 2014	132
Minimum payment in 2015	131
Minimum payment in 2016	94
Minimum payment after 2016	$ 353