Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013 MBbls	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012 MBbls	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 MBbls	Dec. 31, 2012 MBbls	Dec. 31, 2011
Change in asset retirement obligations [Line Items]
Less: Current portion of ARO	$ (54)				$ (10)				$ (54)	$ (10)
Asset Retirement Obligations, Noncurrent	201				132				201	132
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue									891	1,092	729
Disposal Group, Including Discontinued Operation, Operating Expense									689	664	508
Disposal Group, Including Discontinued Operation, Operating Income (Loss)									202	428	221
Discontinued Operation, Amount of Other Income (Loss) from Disposition of Discontinued Operations, before Income Tax									4	(3)	0
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax									206	425	221
Discontinued Operation, Tax Effect of Discontinued Operation									167	707	83
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(14)	31	5	17	(479)	49	71	77	39	(282)	138
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	84				76				84	76
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net	200				207				200	207
Disposal Group, Including Discontinued Operation, Inventory	130				91				130	91
Disposal Group, Including Discontinued Operation, Other Current Assets	33				31				33	31
Assets of Disposal Group, Including Discontinued Operation, Current	447				405				447	405
Disposal Group, including Discontinued Operations, Oil and Gas Properties, Net	989				781				989	781
Disposal Group, Including Discontinued Operation, Other Noncurrent Assets	4				4				4	4
Assets of Disposal Group, Including Discontinued Operation, Noncurrent	1,012				809				1,012	809
Assets of Disposal Group, Including Discontinued Operation	1,459				1,214				1,459	1,214
Disposal Group, Including Discontinued Operation, Deferred Tax Assets	19				24				19	24
Disposal Group, Including Discontinued Operation, Accounts Payable	38				50				38	50
Disposal Group, Including Discontinued Operation, Accrued Liabilities	324				269				324	269
Disposal Group, Including Discontinued Operations, Asset Retirement Obligation, Current	49				5				49	5
Disposal Group, Including Discontinued Operation, Other Current Liabilities	18				16				18	16
Liabilities of Disposal Group, Including Discontinued Operation, Current	429				340				429	340
Disposal Group, Including Discontinued Operations, Asset Retirement Obligations	86				37				86	37
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities	129				41				129	41
Disposal Group, Including Discontinued Operation, Other Noncurrent Liabilities	11				24				11	24
Liabilities of Disposal Group, Including Discontinued Operation, Noncurrent	226				102				226	102
Liabilities of Disposal Group, Including Discontinued Operation	655				442				655	442
Disposal Group, Including Discontinued Operations, Accumulated Depreciation, Depletion and Amortization, Property Plant and Equipment	1,121				843				1,121	843
Effective Income Tax Rate, Discontinuing Operations									81.00%	166.00%	37.00%
Crude oil inventory in barrels	1,100				700				1,100	700
Not subject to amortization, Discontinued Operations	115								115
Energy Related Inventory, Petroleum	90				64				90	64
Unweighted average commodity price of natural gas based on first day of month prices for prior twelve months	3.67				2.76				3.67	2.76	4.12
Unweighted average commodity price of oil based on first day of month prices for prior twelve months	96.82				94.84				96.82	94.84	96.13
Historical Effective Tax Rate, Discontinuing Operations									37.00%
Costs incurred in 2010 and prior not subject to amortization [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Not subject to amortization, Discontinued Operations	45								45
Costs incurred in 2011 not subject to amortization [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Not subject to amortization, Discontinued Operations	2								2
Costs incurred in 2012 not subject to amortization [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Not subject to amortization, Discontinued Operations	24								24
Costs incurred in 2013 not subject to amortization [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Not subject to amortization, Discontinued Operations	44								44
Discontinued Operations, Deferred Tax Expense [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Prior Period Other Adjustment									15
Current [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Tax Effect of Discontinued Operation									90	193	76
Deferred [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Tax Effect of Discontinued Operation									77	514	7
Discontinued Operations [Member]
Change in asset retirement obligations [Line Items]
Beginning Balance				42				39	42	39	12
Accretion expense									3	3	2
Additions									4	4	29
Revisions									101	0	0
Settlements									(15)	(4)	(4)
Ending Balance	135				42				135	42	39
Less: Current portion of ARO	(49)				(5)				(49)	(5)	(6)
Asset Retirement Obligations, Noncurrent	$ 86				$ 37				$ 86	$ 37	$ 33