Restructuring - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	$ 44
Ending Reserve Balance	39
Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	30	$ 30
Ending Reserve Balance	8
Ratings
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	25	6	$ 13
Market and Commodities Intelligence
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded			$ 33
Operating segments | Ratings | Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	25
Ending Reserve Balance	24
Operating segments | Ratings | Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		14
Ending Reserve Balance	4
Operating segments | Market and Commodities Intelligence
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	9
Operating segments | Market and Commodities Intelligence | Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	9
Ending Reserve Balance	5
Operating segments | Market and Commodities Intelligence | Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		10
Ending Reserve Balance	3
Operating segments | Indices | Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	0
Ending Reserve Balance	0
Operating segments | Indices | Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		1
Ending Reserve Balance	0
Corporate | Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	10
Ending Reserve Balance	10
Corporate | Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		$ 5
Ending Reserve Balance	$ 1