Clearing Operations (Narrative) (Details)	1 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2020 USD ($) contract fund	Sep. 30, 2019 USD ($) contract	Dec. 31, 2019 USD ($)
Clearing Operations [Line Items]
Number of member sponsored default funds (in funds) | fund		4
Loss due to commodities market default	$ 133,000,000
Clearing default loss	$ 8,000,000
Capital relief program expense		$ 23,000,000
Default fund contributions		571,000,000
Default fund contributions and margin deposits		8,760,000,000
Liability due to market default		0
Liability Waterfall
Clearing Operations [Line Items]
Junior capital, cash deposits and pledged assets		36,000,000
Senior capital, cash deposits and pledged assets		22,000,000
Committed capital		73,000,000
Utilize as capital resources
Clearing Operations [Line Items]
Default fund contributions		473,000,000
Utilize as member posted surplus balance
Clearing Operations [Line Items]
Default fund contributions		98,000,000
Nasdaq clearing members cash contributions
Clearing Operations [Line Items]
Default fund contributions		482,000,000
Default fund contributions and margin deposits		$ 3,378,000,000		$ 2,996,000,000
Minimum
Clearing Operations [Line Items]
Reverse purchase agreements, maturity range		6 days
Maximum
Clearing Operations [Line Items]
Reverse purchase agreements, maturity range		8 days
Nasdaq Clearing
Clearing Operations [Line Items]
Maturity period of time deposits		90 days
Committed capital		$ 131,000,000
Power of assessment of the clearing member's contribution to the financial markets and commodities markets default funds (as a percent)		230.00%
Contract value of resale and repurchase agreements		$ 2,400,000,000	$ 2,100,000,000
Total number of derivative contracts cleared | contract		3,639,384	5,580,836