Nasdaq Stockholders' Equity (Narrative) (Details)	1 Months Ended	3 Months Ended
	Apr. 30, 2021 USD ($) $ / shares	Mar. 31, 2021 USD ($) vote $ / shares shares	Dec. 31, 2020 vote $ / shares shares	Mar. 31, 2020 $ / shares shares	Jan. 31, 2021 USD ($)
Stockholders Equity [Line Items]
Common stock, shares authorized (in shares)		300,000,000	300,000,000
Common stock, shares issued (in shares)		170,860,750	171,278,761
Common stock, shares outstanding (in shares)		164,242,471	164,933,678
Common stock (in votes per share) | vote		1	1
Common stock holder voting rights, maximum percentage of the then-outstanding shares of Nasdaq common stock		5.00%	5.00%
Common stock in treasury (in shares)		6,618,279	6,345,083
Authorized amount under share repurchase program | $		$ 248,000,000
Additional amount under stock repurchase program | $					$ 1,000,000,000
Number of shares of common stock repurchased (in shares)		1,121,620
Preferred stock, shares authorized (in shares)		30,000,000	30,000,000
Preferred stock par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01
Preferred stock, shares issued (in shares)		0		0
Preferred stock, shares outstanding (in shares)		0		0
Payments of dividends | $		$ 81,000,000
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 0.49	$ 0.49	$ 0.47
Subsequent Event
Stockholders Equity [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares	$ 0.54
Percentage increase in common stock dividend	0.10
Dividends declared | $	$ 89,000,000
Other Repurchases of Common Stock
Stockholders Equity [Line Items]
Number of shares of common stock repurchased (in shares)		273,196