Segment and Geographic Information - Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment information
Revenue	$ 1,536	$ 1,546	$ 1,609	$ 1,567	$ 1,589	$ 1,513	$ 1,509	$ 1,453	$ 6,258	$ 6,063	$ 5,661
Operating Profit	704	$ 704	$ 672	$ 711	627	$ 649	$ 668	$ 639	2,790	2,583	3,341
Amortization of intangibles									122	98	96
Pre-tax gain (loss) on dispositions											1,100
Depreciation & Amortization									206	180	181
Capital Expenditures									113	123	115
Total Assets	9,458				9,425				9,458	9,425
Assets held for sale	14				5				14	5
Operating segments
Segment information
Operating Profit									3,021	2,778	3,488
Depreciation & Amortization									167	171	173
Capital Expenditures									84	100	102
Total Assets	6,516				6,230				6,516	6,230
Corporate
Segment information
Revenue									15	0	0
Operating Profit									(231)	(195)	(147)
Employee severance charges									10	10
Amortization of intangibles									23
Non-cash acquisition and disposition-related costs/adjustments									31
Pre-tax gain (loss) on dispositions											3
Lease exit costs										19
Asset write-off									11
Depreciation & Amortization									39	9	8
Capital Expenditures									29	23	13
Total Assets	2,928				3,190				2,928	3,190
Intersegment elimination
Segment information
Revenue									(125)	(110)	(98)
Ratings
Segment information
Legal fees									74
Employee severance charges									8	25	6
Legal settlement insurance recoveries										55	10
Amortization of intangibles									2	4	5
Total Assets	680				788				680	788
Ratings | Operating segments
Segment information
Revenue									2,883	2,988	2,535
Operating Profit									1,530	1,517	1,256
Depreciation & Amortization									32	34	34
Capital Expenditures									42	45	42
Market Intelligence
Segment information
Employee severance charges										7
Amortization of intangibles									73	71	72
Business disposition and employee severance charges									7
Non-cash acquisition and disposition-related costs/adjustments										4	43
Pre-tax gain (loss) on dispositions											373
Impairment of intangible assets											24
Acquisition-related costs											1
Total Assets	3,606				3,381				3,606	3,381
Market Intelligence | Operating segments
Segment information
Revenue									1,833	1,683	1,661
Operating Profit									545	457	729
Depreciation & Amortization									99	104	105
Capital Expenditures									30	37	40
Platts
Segment information
Employee severance charges										2
Amortization of intangibles									18	18	14
Non-cash acquisition and disposition-related costs/adjustments										11	5
Pre-tax gain (loss) on dispositions											728
Lease exit costs										6
Asset write-off										2
Total Assets	787				791				787	791
Platts | Operating segments
Segment information
Revenue									815	774	925
Operating Profit									383	326	1,090
Depreciation & Amortization									27	25	26
Capital Expenditures									9	15	17
Indices
Segment information
Amortization of intangibles									6	6	6
Total Assets	$ 1,443				$ 1,270				1,443	1,270
Indices | Operating segments
Segment information
Revenue									837	728	638
Operating Profit									563	478	413
Depreciation & Amortization									9	8	8
Capital Expenditures									$ 3	$ 3	$ 3