Goodwill and Acquired Intangible Assets (Schedule of Changes in Goodwill) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 6,366
Goodwill acquired	134
Foreign currency translation adjustment	100
Balance at end of period	6,600
Market Services
Goodwill [Roll Forward]
Balance at beginning of period	3,342
Goodwill acquired	0
Foreign currency translation adjustment	49
Balance at end of period	3,391
Corporate Services
Goodwill [Roll Forward]
Balance at beginning of period	460
Goodwill acquired	0
Foreign currency translation adjustment	5
Balance at end of period	465
Information Services
Goodwill [Roll Forward]
Balance at beginning of period	2,283
Goodwill acquired	134
Foreign currency translation adjustment	40
Balance at end of period	2,457
Market Technology
Goodwill [Roll Forward]
Balance at beginning of period	281
Goodwill acquired	0
Foreign currency translation adjustment	6
Balance at end of period	$ 287