Nasdaq Stockholders' Equity (Schedule of Dividends Declared) (Details) - USD ($) $ / shares in Units, $ in Millions							3 Months Ended		9 Months Ended
	Sep. 11, 2020	Jul. 22, 2020	Jun. 12, 2020	Apr. 22, 2020	Mar. 13, 2020	Jan. 28, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Dividends Payable [Line Items]
Dividend Per Common Share (in dollars per share)		$ 0.49					$ 0.49	$ 0.47	$ 1.45	$ 1.38
Total Amount Paid	$ 81								$ 239
Dividend Declaration Date First Quarter
Dividends Payable [Line Items]
Dividend Per Common Share (in dollars per share)						$ 0.47
Total Amount Paid					$ 78
Dividend Declaration Date Second Quarter
Dividends Payable [Line Items]
Dividend Per Common Share (in dollars per share)				$ 0.49
Total Amount Paid			$ 80