Restructuring - Summary (Details) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) position
Market Intelligence
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	$ 4		$ 4
Platts
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded	$ 1		$ 1
2017 Restructuring Plans
Restructuring Cost and Reserve [Line Items]
Workforce reduction | position				520
Initial Charge Recorded		$ 44
Ending Reserve Balance		22		$ 39
Restructuring charges paid		17
Operating Segments | 2017 Restructuring Plans | Ratings
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		25
Ending Reserve Balance		15
Operating Segments | 2017 Restructuring Plans | Market Intelligence
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		8
Ending Reserve Balance		2
Operating Segments | 2017 Restructuring Plans | Platts
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		1
Ending Reserve Balance		0
Operating Segments | 2017 Restructuring Plans | Indices
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		0
Ending Reserve Balance		0
Corporate | 2017 Restructuring Plans
Restructuring Cost and Reserve [Line Items]
Initial Charge Recorded		10
Ending Reserve Balance		$ 5