Commitment and Contingencies - Summary of Information Concerning Our Recorded Liabilities For Environmental Costs (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
December 31, 2017	$ 537
Accruals for environmental matters deemed probable and reasonably estimable	322
Environmental liability remediated	(124)
September 30, 2018	$ 735

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Amount of expense for newly incurred environmental loss contingencies. Includes, but is not limited to, remediation expense and interest accretion.

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Amount of cash outflow to settle environmental loss contingencies.

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