Revenue Recognition - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) obligation	Sep. 30, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Number of performance obligations | obligation			2
Number of performance obligations related to trade execution | obligation			1
Rebates	$ 218	$ 183	$ 653	$ 615
Total revenues	1,663	1,463	4,880	4,599
Interest rates and other financial futures and options contracts
Disaggregation of Revenue [Line Items]
Total revenues	929	760	2,698	2,522
Trading and Clearing Segment
Disaggregation of Revenue [Line Items]
Total revenues	996	821	2,892	2,691
Trading and Clearing Segment | Interest rates and other financial futures and options contracts
Disaggregation of Revenue [Line Items]
Total revenues	929	760	2,698	2,522
Trading and Clearing Segment | Interest rates and other financial futures and options contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenues	$ 66	$ 56	$ 188	$ 184