Segment Reporting - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Revenues, less transaction-based expenses	$ 1,178	$ 1,129	$ 2,342	$ 2,283
Operating expenses	569	578	1,151	1,148
Operating income	609	551	1,191	1,135
Trading and Clearing Segment
Segment Reporting Information [Line Items]
Revenues, less transaction-based expenses	550	527	1,088	1,101
Operating expenses	214	214	430	427
Operating income	336	313	658	674
Data and Listings Segment
Segment Reporting Information [Line Items]
Revenues, less transaction-based expenses	628	602	1,254	1,182
Operating expenses	355	364	721	721
Operating income	$ 273	$ 238	$ 533	$ 461
Customer Concentration Risk | Sales Revenue, Segment | One Clearing
Segment Reporting Information [Line Items]
Concentration risk, percentage	10.00%		10.00%	10.00%