Discontinued Operations (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Discontinued Operations
Gain on the disposal of the discontinued operations before tax	$ 12	$ (4)	$ 173	$ 181
Proceeds from disposal of discontinued operations, net				284
Summarized results of discontinued operations
Operating revenues				62	110	115
Costs and expenses				(55)	(99)	(110)
Loss on impairment				(10)	(2)
Income (loss) from discontinued operations before income tax expense				178	9	5
Income tax benefit (expense)				19	25	(31)
Income from discontinued operations, net of tax				197	34	(26)
Impairment loss per diluted share from discontinued operations				$ 0.03	$ 0.01
Assets
Oil and gas properties, net	24			24
Other related assets	2			2
Assets held for sale	26			26
Accounts receivable	6			6	22
Other assets	25			25	17
Other current assets	31			31	39
Rig and related equipment, net					86
Oil and gas properties, net					53
Other assets					139
Liabilities
Accounts payable	3			3	15
Other liabilities	14			14	13
Other current liabilities	17			17	28
Asset retirement obligation					9
Deferred taxes					19
Other long-term liabilities					28
Challenger Minerals
Discontinued Operations
Gain on the disposal of the discontinued operations before tax				12
Proceeds from disposal of discontinued operations, net	24
Caspian Sea Operations
Discontinued Operations
Proceeds from disposal of discontinued operations, net				259
Gain on disposal of the discontinued operations per diluted share				$ 0.52
Summarized results of discontinued operations
Gain on disposal of discontinued operations, net of tax				$ 169