Acquisitions - Narrative (Details) - USD ($) $ in Millions				9 Months Ended
	Sep. 15, 2021	Mar. 19, 2021	Feb. 13, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill				$ 5,898		$ 4,556	$ 3,722
MA
Business Acquisition [Line Items]
Goodwill				5,502		4,245	3,407
MIS
Business Acquisition [Line Items]
Goodwill				396		$ 311	$ 315
RMS
Business Acquisition [Line Items]
Business acquisition interests acquired	100.00%
Total consideration	$ 1,936
Goodwill	1,389
Indemnification asset, amount	88
Transaction costs	22
RMS | Fair Value Adjustment to Deferred Revenue
Business Acquisition [Line Items]
Revenues				$ 3	$ (21)
RMS | MA
Business Acquisition [Line Items]
Goodwill	1,299
RMS | MIS
Business Acquisition [Line Items]
Goodwill	$ 90
Cortera
Business Acquisition [Line Items]
Business acquisition interests acquired		100.00%
Total consideration		$ 139
Goodwill		$ 79
Regulatory Data Corporation
Business Acquisition [Line Items]
Business acquisition interests acquired			100.00%
Total consideration			$ 702
Goodwill			$ 494