Revenue From Contracts With Customers (Revenue by Product, Service and Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	$ 715	$ 632	$ 2,115	$ 1,889
Transaction-based trading and clearing, net
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	183	154	596	468
Trade management services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	76	72	221	219
Listing services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	79	74	228	219
Corporate solutions
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	53	50	158	149
Market data
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	107	102	305	302
Index
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	86	56	227	166
Investment data & analytics
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	45	40	129	117
Market technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	86	84	251	239
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	259	226	817	687
Operating Segments | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	132	124	386	368
Operating Segments | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	238	198	661	585
Operating Segments | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	86	84	251	239
Operating Segments | Transaction-based trading and clearing, net | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	183	154	596	468
Operating Segments | Transaction-based trading and clearing, net | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Transaction-based trading and clearing, net | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Transaction-based trading and clearing, net | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Trade management services | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	76	72	221	219
Operating Segments | Trade management services | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Trade management services | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Trade management services | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Listing services | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Listing services | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	79	74	228	219
Operating Segments | Listing services | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Listing services | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Corporate solutions | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Corporate solutions | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	53	50	158	149
Operating Segments | Corporate solutions | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Corporate solutions | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market data | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market data | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market data | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	107	102	305	302
Operating Segments | Market data | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Index | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Index | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Index | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	86	56	227	166
Operating Segments | Index | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Investment data & analytics | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Investment data & analytics | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Investment data & analytics | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	45	40	129	117
Operating Segments | Investment data & analytics | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market technology | Market Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market technology | Corporate Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market technology | Information Services
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	0	0	0	0
Operating Segments | Market technology | Market Technology
Disaggregation of Revenue [Line Items]
Revenues less transaction-based expenses	$ 86	$ 84	$ 251	239
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