Revenues - Revenues Disaggregated by Line of Business and Geographical Area (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,786	$ 1,470
United States
Disaggregation of Revenue [Line Items]
Revenue	969	763
Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	817	707
MA
Disaggregation of Revenue [Line Items]
Revenue	799	737
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	802	740
MA | United States
Disaggregation of Revenue [Line Items]
Revenue	337	317
MA | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	337	317
MA | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	462	420
MA | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	462	420
MA | Decision Solutions (DS)
Disaggregation of Revenue [Line Items]
Revenue	365	334
MA | Decision Solutions (DS) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	365	334
MA | Decision Solutions (DS) | United States
Disaggregation of Revenue [Line Items]
Revenue	138	132
MA | Decision Solutions (DS) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	227	202
MA | Research and Insights (R&I)
Disaggregation of Revenue [Line Items]
Revenue	222	215
MA | Research and Insights (R&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	222	215
MA | Research and Insights (R&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	122	118
MA | Research and Insights (R&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	100	97
MA | Data and Information (D&I)
Disaggregation of Revenue [Line Items]
Revenue	212	188
MA | Data and Information (D&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	212	188
MA | Data and Information (D&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	77	67
MA | Data and Information (D&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	135	121
MIS
Disaggregation of Revenue [Line Items]
Revenue	987	733
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,034	778
MIS | United States
Disaggregation of Revenue [Line Items]
Revenue	632	446
MIS | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	632	446
MIS | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	355	287
MIS | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	355	287
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	529	356
MIS | Corporate Finance (CFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	529	356
MIS | Corporate Finance (CFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	372	246
MIS | Corporate Finance (CFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	157	110
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	114	99
MIS | Structured Finance (SFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	114	99
MIS | Structured Finance (SFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	76	61
MIS | Structured Finance (SFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	38	38
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	195	142
MIS | Financial Institutions (FIG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	195	142
MIS | Financial Institutions (FIG) | United States
Disaggregation of Revenue [Line Items]
Revenue	98	63
MIS | Financial Institutions (FIG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	97	79
MIS | Public, Project and Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	141	129
MIS | Public, Project and Infrastructure Finance (PPIF) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	141	129
MIS | Public, Project and Infrastructure Finance (PPIF) | United States
Disaggregation of Revenue [Line Items]
Revenue	86	76
MIS | Public, Project and Infrastructure Finance (PPIF) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	55	53
MIS | Total ratings revenue
Disaggregation of Revenue [Line Items]
Revenue	979	726
MIS | Total ratings revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	979	726
MIS | Total ratings revenue | United States
Disaggregation of Revenue [Line Items]
Revenue	632	446
MIS | Total ratings revenue | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	347	280
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	8	7
MIS | MIS Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	8	7
MIS | MIS Other | United States
Disaggregation of Revenue [Line Items]
Revenue	0	0
MIS | MIS Other | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	$ 8	$ 7