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Impairments and Assets Held For Sale (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Segment Reporting Information [Line Items]      
Document Period End Date Dec. 31, 2020    
Income tax benefit $ (4) $ (10) $ (13)
Assets held for sale   25  
Depreciation and amortization 554 647 690
Gain on sale of assets $ 0 $ (6) $ 16