Provision (Benefit) for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Feb. 28, 2013 Internal Revenue Service (IRS) [Member]
Current :
Federal	$ 25		$ 58	$ (47)	$ 112
State	0		10	3	18
Foreign	2		6	3	30
Total	27		74	(41)	160
Deferred:
Federal	21		6	233	123
State	9		(3)	41	(9)
Foreign	5		0	27	7
Total	35		3	301	121
Provision (benefit) for income taxes	62		77	260	281
Income Tax Contingency [Line Items]
Tax provision (benefit) from income tax examination			2		2
Cash payment (refund) from income tax examination							12
Tax settlements with WPX						2
Deferred tax provison related to change in tax law		10
Estimated Deferred IncomeTax Expense To Be Recognized Related To Proposed Transaction	200
Estimated Current Tax Liablity Upon Completion Of Proposed Transaction	140			140
Provision For Income Taxes From Continuing Operations At Federal Statutory Rate [Abstract]
Provision (benefit) for income taxes	$ 62		$ 77	$ 260	$ 281