Nature of Operations and Basis of Presentation - Narrative (Details) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
		Apr. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Segment	Sep. 30, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Number of reportable segments | Segment					4
Disaggregation of Revenue [Line Items]
Retained income			$ 11,003		$ 11,003			$ 10,025
Revenue from contract with customer, excluding assessed tax			1,546	$ 1,513	4,721	$ 4,475
Contract asset			43		43			$ 17
Revenue expected to be recognized as of March 31, 2018			1,200		1,200
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Disaggregation of Revenue [Line Items]
Retained income							$ 35
Revenue from contract with customer, excluding assessed tax					5
Accounts receivable, net							$ 1,319
Unearned revenue					1,400
Capitalized contract costs			82		82
Kensho
Disaggregation of Revenue [Line Items]
Consideration transferred to acquire business	[1]	$ 550
Restricted cash	[1]	$ 37
Intersegment Elimination
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			$ (32)	(28)	$ (92)	(81)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction of remaining performance obligation			1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction of remaining performance obligation			1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction of remaining performance obligation
Non-transaction
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			$ 340	339	$ 1,037	980
Non-transaction | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			$ (32)	$ (28)	$ (92)	$ (81)

[1] Excludes $112 million attributable to our redeemable noncontrolling interest.