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Consolidated Balance Sheets (Parentheticals) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Allowance for doubtful accounts $ 93 $ 124
Accumulated depreciation $ 1,457 $ 1,544
Common stock par value $ 0.01 $ 0.01
Common Stock, Shares Authorized 1 1