Asset Retirement Obligations and Accrued Environmental Costs (Asset Retirement Obligations and Accrued Environmental Costs) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligations and Accrued Environmental Costs [Abstract]
Asset retirement obligations	$ 5,926	$ 5,573	$ 6,206
Accrued environmental costs	187	180
Total asset retirement obligations and accrued environmental costs	6,113	5,753
Asset retirement obligations and accrued environmental costs due within one year	(359)	(323)
Long-term asset retirement obligations and accrued environmental costs	$ 5,754	$ 5,430