Revenue From Contracts With Customers (Revenue by Product, Service and Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	$ 701	$ 634
Transaction-based trading and clearing, net
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	209	160
Trade management services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	72	73
Listing services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	75	71
Corporate solutions
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	53	50
Market data
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	97	100
Index
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	73	54
Investment data & analytics
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	41	39
Market technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	81	77
Other revenues
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		10
Operating Segments | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	281	233
Operating Segments | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	128	121
Operating Segments | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	211	193
Operating Segments | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	81	77
Operating Segments | Transaction-based trading and clearing, net | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	209	160
Operating Segments | Transaction-based trading and clearing, net | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Transaction-based trading and clearing, net | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Transaction-based trading and clearing, net | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Trade management services | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	72	73
Operating Segments | Trade management services | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Trade management services | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Trade management services | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Listing services | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Listing services | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	75	71
Operating Segments | Listing services | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Listing services | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Corporate solutions | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Corporate solutions | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	53	50
Operating Segments | Corporate solutions | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Corporate solutions | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market data | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market data | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market data | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	97	100
Operating Segments | Market data | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Index | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Index | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Index | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	73	54
Operating Segments | Index | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Investment data & analytics | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Investment data & analytics | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Investment data & analytics | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	41	39
Operating Segments | Investment data & analytics | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market technology | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market technology | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market technology | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0
Operating Segments | Market technology | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	$ 81	77
Operating Segments | Other revenues | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Operating Segments | Other revenues | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Operating Segments | Other revenues | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Operating Segments | Other revenues | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		10
Other Revenues | Transaction-based trading and clearing, net
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Trade management services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Listing services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Corporate solutions
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Market data
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Index
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Investment data & analytics
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Market technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		0
Other Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses		$ 10