Nature of Operations and Basis of Presentation - Narrative (Details) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
		Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Segment	Jun. 30, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable segments | Segment					4
Disaggregation of Revenue [Line Items]
Retained income			$ 10,680		$ 10,680			$ 10,025
Revenue from contract with customer, excluding assessed tax			1,609	$ 1,509	3,176	$ 2,962
Contract asset			28		28			$ 17
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			3		6
Intersegment revenue			32	$ 28	60	$ 53
Accounts receivable, net							$ 1,319
Unearned revenue					1,100
Revenue expected to be recognized as of March 31, 2018			1,100		1,100
Capitalized contract costs			$ 79		$ 79
Minimum | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Disaggregation of Revenue [Line Items]
Expected timing of satisfaction of remaining performance obligation			12 months		12 months
Maximum | Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Disaggregation of Revenue [Line Items]
Expected timing of satisfaction of remaining performance obligation			24 months		24 months
Kensho
Disaggregation of Revenue [Line Items]
Consideration transferred to acquire business	[1]	$ 550
Restricted cash	[1]	$ 43

[1] Excludes $76 million attributable to our redeemable noncontrolling interest.