Goodwill and Acquired Intangible Assets (Schedule of Changes in Goodwill) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 6,366
Goodwill acquired	133
Foreign currency translation adjustment	(173)
Balance at end of period	6,326
Market Services
Goodwill [Roll Forward]
Balance at beginning of period	3,342
Goodwill acquired	0
Foreign currency translation adjustment	(91)
Balance at end of period	3,251
Corporate Services
Goodwill [Roll Forward]
Balance at beginning of period	460
Goodwill acquired	0
Foreign currency translation adjustment	(10)
Balance at end of period	450
Information Services
Goodwill [Roll Forward]
Balance at beginning of period	2,283
Goodwill acquired	133
Foreign currency translation adjustment	(51)
Balance at end of period	2,365
Market Technology
Goodwill [Roll Forward]
Balance at beginning of period	281
Goodwill acquired	0
Foreign currency translation adjustment	(21)
Balance at end of period	$ 260