Income Taxes - Net Deferred Tax Liability (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Deferred income	$ (33)	$ (89)
Federal and state net operating loss carryforwards	(932)	(236)
Foreign net operating loss carryforwards	(61)	(55)
Tax credits	(78)	(66)
Accrued expenses and liabilities	(2)	(90)
Total deferred tax assets	(1,106)	(536)
Valuation allowance	419	60
Net deferred tax assets	(687)	(476)
Deferred tax liabilities:
Other	23	21
Depreciation, depletion and amortization	8,536	7,443
Total deferred tax liabilities	8,559	7,464
Net deferred income tax liability	$ 7,872	$ 6,988