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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Company Before Tax Obligation      
Balance at January 1 $ 13,616 $ 12,832 $ 14,050
Liabilities assumed in the Noble acquisition 0 630 0
Liabilities incurred 31 10 32
Liabilities settled (1,887) (1,661) (1,694)
Accretion expense 616 560 628
Revisions in estimated cash flows 432 1,245 (184)
Balance at December 31 12,808 $ 13,616 $ 12,832
Long-term portion of the company's before-tax asset retirement obligations $ 11,611