Revenues - Revenues Disaggregated by Line of Business and Geographical Area (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 1,522	$ 1,600
United States
Disaggregation of Revenue [Line Items]
Revenue	862	885
Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	660	715
MIS
Disaggregation of Revenue [Line Items]
Revenue	827	1,036
MIS | United States
Disaggregation of Revenue [Line Items]
Revenue	513	647
MIS | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	314	389
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	417	605
MIS | Corporate Finance (CFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	275	414
MIS | Corporate Finance (CFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	142	191
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	144	116
MIS | Structured Finance (SFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	97	68
MIS | Structured Finance (SFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	47	48
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	131	162
MIS | Financial Institutions (FIG) | United States
Disaggregation of Revenue [Line Items]
Revenue	65	86
MIS | Financial Institutions (FIG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	66	76
MIS | Public, Project And Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	123	143
MIS | Public, Project And Infrastructure Finance (PPIF) | United States
Disaggregation of Revenue [Line Items]
Revenue	75	78
MIS | Public, Project And Infrastructure Finance (PPIF) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	48	65
MIS | Rating Revenue
Disaggregation of Revenue [Line Items]
Revenue	815	1,026
MIS | Rating Revenue | United States
Disaggregation of Revenue [Line Items]
Revenue	512	646
MIS | Rating Revenue | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	303	380
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	12	10
MIS | MIS Other | United States
Disaggregation of Revenue [Line Items]
Revenue	1	1
MIS | MIS Other | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	11	9
MA
Disaggregation of Revenue [Line Items]
Revenue	695	564
MA | United States
Disaggregation of Revenue [Line Items]
Revenue	349	238
MA | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	346	326
MA | Decision Solutions
Disaggregation of Revenue [Line Items]
Revenue	334	225
MA | Decision Solutions | United States
Disaggregation of Revenue [Line Items]
Revenue	188	91
MA | Decision Solutions | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	146	134
MA | Research and Insights
Disaggregation of Revenue [Line Items]
Revenue	183	171
MA | Research and Insights | United States
Disaggregation of Revenue [Line Items]
Revenue	101	92
MA | Research and Insights | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	82	79
MA | Data and Information
Disaggregation of Revenue [Line Items]
Revenue	178	168
MA | Data and Information | United States
Disaggregation of Revenue [Line Items]
Revenue	60	55
MA | Data and Information | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	$ 118	$ 113