Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,786	$ 1,470
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(50)	(48)
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(50)	(48)
MA
Disaggregation of Revenue [Line Items]
Revenue	799	737
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	802	740
MA | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	3	3
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) | DS Banking Product and Service | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	134	131
MA | Decision Solutions (DS) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	144	133
MA | Decision Solutions (DS) | KYC | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	87	70
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 | 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
MIS
Disaggregation of Revenue [Line Items]
Revenue	987	733
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,034	778
MIS | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	47	45
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) | Investment-grade | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	147	115
MIS | Corporate Finance (CFG) | High-yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	67	32
MIS | Corporate Finance (CFG) | Bank loans | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	155	59
MIS | Corporate Finance (CFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	160	150
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) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1	1
MIS | Structured Finance (SFG) | Asset-backed securities | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	33	27
MIS | Structured Finance (SFG) | RMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	24	25
MIS | Structured Finance (SFG) | CMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	17	14
MIS | Structured Finance (SFG) | Structured credit | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	39	32
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) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	59	33
MIS | Financial Institutions (FIG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3	3
MIS | Financial Institutions (FIG) | Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	121	100
MIS | Financial Institutions (FIG) | Managed investments | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	12	6
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) | Public finance / sovereign | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	59	52
MIS | Public, Project and Infrastructure Finance (PPIF) | Project and infrastructure | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	82	77
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 | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	8	7
MIS | MIS Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	$ 8	$ 7