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Consolidated Balance Sheets (Parentheticals) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Allowance for doubtful accounts $ 87 $ 91
Accumulated depreciation $ 1,235 $ 1,174
Common stock par value $ 0.01 $ 0.01
Common Stock, Shares Authorized 1 1