Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation Beginning Balance	$ 1,783	[1]	$ 1,510
Incurred, including acquisitions	84		150
Settled, including dispositions	(78)		(35)
Accretion expense (included in depreciation, depletion and amortization)	106		91
Revisions to previous estimates	244		150
Held for sale	(43)		(83)
Asset Retirement Obligation Ending Balance	2,096	[1]	1,783	[1]
Asset Retirement Obligation, Current	$ 87		$ 34

[1] Includes asset retirement obligations of $87 million and $34 million classified as short-term at December 31, 2013 and 2012.