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CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares
shares in Millions
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Dec. 31, 2017
Treasury stock, shares 1 1    
Class A common stock        
Common stock, shares issued 164 163 174 173
Class B common stock        
Common stock, shares issued 697 696 689 687