Clearing Operations (Narrative) (Details)	1 Months Ended	3 Months Ended
	Sep. 30, 2018 USD ($)	Mar. 31, 2020 USD ($) fund contract	Mar. 31, 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		505,000,000
Default fund contributions and margin deposits		7,299,000,000
Committed capital		254,000,000		$ 291,000,000
Liability due to market default		0
Liability Waterfall
Clearing Operations [Line Items]
Junior capital, cash deposits and pledged assets		33,000,000
Senior capital, cash deposits and pledged assets		20,000,000
Committed capital		88,000,000
Utilize as capital resources
Clearing Operations [Line Items]
Default fund contributions		400,000,000
Utilize as member posted surplus balance
Clearing Operations [Line Items]
Default fund contributions		105,000,000
Cash Contributions
Clearing Operations [Line Items]
Default fund contributions		414,000,000
Default fund contributions and margin deposits		$ 3,241,000,000		$ 2,996,000,000
Minimum
Clearing Operations [Line Items]
Reverse purchase agreements, maturity range		1 day
Maximum
Clearing Operations [Line Items]
Reverse purchase agreements, maturity range		14 days
Nasdaq Clearing
Clearing Operations [Line Items]
Maturity period of time deposits		90 days
Committed capital		$ 141,000,000
Power of assessment of the clearing member's contribution to the financial markets and commodities markets default funds (as a percent)		100.00%
Contract value of resale and repurchase agreements		$ 1,000,000,000.0	$ 5,500,000,000
Total number of derivative contracts cleared | contract		1,410,884	1,885,698