Nasdaq Stockholders' Equity (Narrative) (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2020 USD ($) $ / shares	Mar. 31, 2020 USD ($) vote $ / shares shares	Mar. 31, 2019 $ / shares shares	Dec. 31, 2019 shares
Stockholders Equity [Line Items]
Common stock, shares authorized (in shares)		300,000,000		300,000,000
Common stock, shares issued (in shares)		170,589,846		171,075,011
Common stock, shares outstanding (in shares)		164,337,766		165,094,440
Common stock (in votes per share) | vote		1
Common stock holder voting rights, maximum percentage of the then-outstanding shares of Nasdaq common stock		5.00%
Common stock in treasury (in shares)		6,252,080		5,980,571
Authorized amount under share repurchase program | $		$ 510
Number of shares of common stock repurchased (in shares)		1,182,114
Preferred stock, shares authorized (in shares)		30,000,000
Preferred stock par value (in dollars per share) | $ / shares		$ 0.01
Preferred stock, shares issued (in shares)		0	0
Preferred stock, shares outstanding (in shares)		0	0
Payments of dividends | $		$ 78
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 0.47	$ 0.44
Cash dividends paid per common share (in dollars per share) | $ / shares			$ 0.47
Subsequent Event
Stockholders Equity [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares	$ 0.49
Dividends declared | $	$ 81
Increase in common stock dividends	4.00%
Other Repurchases of Common Stock
Stockholders Equity [Line Items]
Number of shares of common stock repurchased (in shares)		271,509