Asset Retirement Obligations and Accrued Environmental Costs (Summary of Asset Retirement Obligations and Accrued Environmental Costs) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Asset Retirement Obligation and Accrual for Environmental Cost Disclosure [Abstract]
Asset retirement obligations	$ 314		$ 378		$ 332
Accrued environmental costs	530		542
Total asset retirement obligations and accrued environmental costs	844		920
Asset retirement obligations and accrued environmental costs due within one year	(104)	[1]	(133)	[1]
Long-term asset retirement obligations and accrued environmental costs	$ 740		$ 787

[1] Classified as a current liability on the balance sheet, under the caption “Other accruals.”