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Nasdaq Stockholders' Equity (Common Stock in Treasury) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Equity [Abstract]      
Number of shares of common stock repurchased (in shares) 4,508,426 2,843,519  
Average price paid per share (in dollars per share) $ 87.43 $ 71.56  
Total purchase price $ 394 $ 203 $ 100