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Drilling Fleet (Impairment held for sale) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Drilling Fleet      
Aggregate loss on impairment of assets held for sale $ 556 $ 578 $ 999
Loss associated with impairment, net of tax (per share) $ 0.90 $ 0.94 $ 2.13
Aggregate loss on impairment of assets held for sale, tax effect $ 0 $ 0 $ 0