Acquisitions and Divestitures - Acquisitions Narrative (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2018	Jan. 31, 2018	Aug. 31, 2017	Jun. 30, 2017	Jun. 30, 2016
Business Acquisition [Line Items]
Consideration paid for acquisition, net of cash acquired		$ 0
Cash paid for acquisitions, net of cash acquired			$ 83	$ 177
Payments for previous acquisition		$ 0	$ 0	$ 5
FiscalNote
Business Acquisition [Line Items]
Cost method investment ownership interest (as a percent)					5.03%
Kensho Technologies
Business Acquisition [Line Items]
Consideration paid for acquisition, net of cash acquired	$ 550
Cost method investment ownership interest (as a percent)				2.54%
Pragmatix Services Private Limited
Business Acquisition [Line Items]
Ownership in equity method investment (as a percent)						100.00%
Algomi Limited
Business Acquisition [Line Items]
Cost method investment ownership interest (as a percent)							6.02%
CARE Ratings Limited
Business Acquisition [Line Items]
Cost method investment ownership interest (as a percent)								8.90%
TRIS Rating Company Limited
Business Acquisition [Line Items]
Cost method investment ownership interest (as a percent)									49.00%
PIRA Energy Group
Business Acquisition [Line Items]
Payments for previous acquisition				$ 34
UCG
Business Acquisition [Line Items]
Payments for previous acquisition				$ 5
Series of Individually Immaterial Business Acquisitions | Minimum
Business Acquisition [Line Items]
Amortization period of acquired intangible assets (in years)		1 year		3 years
Series of Individually Immaterial Business Acquisitions | Maximum
Business Acquisition [Line Items]
Amortization period of acquired intangible assets (in years)		10 years		10 years