Nasdaq Stockholders' Equity (Common Stock in Treasury) (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Equity [Abstract]
Number of shares of common stock repurchased (in shares)	1,752,474	2,053,855
Average price paid per share (in dollars per share)	$ 106.26	$ 97.37
Total purchase price (in millions)	$ 186	$ 200

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the par value method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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