Debt (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Debt	$ 2,830		$ 2,279
Unamortized discount	(12)		(7)
Total debt, net of discount	2,818		2,272
Less amounts due within one year (1)	(21)	[1]	0	[1]
Long-term debt due after one year	2,797		2,272
Debt issuance proceeds used to repay outstanding indebtedness	470
2011	0
2012	0
2013	0
2014	200
2015	0
Thereafter	2,284
Total	2,484
2011	0
2012	72
2013	72
2014	72
2015	72
Thereafter	209
Total	497
Credit Facility due December 9 2012 [Member]
Debt Instrument [Line Items]
Debt	0		350
Interest rate (in hundredths)	0.00%		0.57%
Debt instrument, maturity date	Dec. 09, 2012
Senior Notes due April 15, 2014 [Member]
Debt Instrument [Line Items]
Debt	200		200
Interest rate (in hundredths)	5.25%		5.25%
Debt instrument, maturity date	Apr. 15, 2014
Senior Notes due March 1, 2019 [Member]
Debt Instrument [Line Items]
Debt	1,000		1,000
Interest rate (in hundredths)	8.25%		8.25%
Debt instrument, maturity date	Mar. 01, 2019
Notes, due October 15, 2023 [Member]
Debt Instrument [Line Items]
Debt	100		100
Interest rate (in hundredths)	7.25%		7.25%
Debt instrument, maturity date	Oct. 15, 2023
Senior Notes due April 1, 2027 [Member]
Debt Instrument [Line Items]
Debt	250		250
Interest rate (in hundredths)	8.00%		8.00%
Debt instrument, maturity date	Apr. 01, 2027
Senior Notes due March 1, 2041 [Member]
Debt Instrument [Line Items]
Debt	850		0
Interest rate (in hundredths)	6.00%		0.00%
Debt instrument, maturity date	Mar. 01, 2041
Debt offering closing date	2011-02-18
Debt offerings proceeds, net of discount and underwriting fees	836
Debt offering face amount	850
Debt issuance costs	9
Senior Notes due August 1, 2097 [Member]
Debt Instrument [Line Items]
Debt	84		84
Interest rate (in hundredths)	7.25%		7.25%
Debt instrument, maturity date	Aug. 01, 2097
FPSO Lease Obligation [Member]
Debt Instrument [Line Items]
Debt	$ 346	[1]	$ 295	[1]
Interest rate (in hundredths)	0.00%		0.00%

[1] We have entered into an agreement to lease a floating production, storage and offloading vessel (FPSO) to be used in the development of the Aseng field, offshore Equatorial Guinea. The amount of the FPSO lease obligation is based on the percentage of construction activities completed as of the reporting dates, and therefore does not reflect future minimum lease obligations. The increase in the FPSO lease obligation is a non-cash financing activity. Amounts due within one year equal the amount by which the FPSO lease obligation is expected to be reduced during the next 12 months as lease payments begin. We currently expect production to commence, at year-end 2011