Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 1,470	$ 1,522
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(48)	(45)
MA
Disaggregation of Revenue [Line Items]
Revenue	737	695
MA | Decision Solutions
Disaggregation of Revenue [Line Items]
Revenue	354	334
MA | Research and Insights
Disaggregation of Revenue [Line Items]
Revenue	195	183
MA | Data and Information
Disaggregation of Revenue [Line Items]
Revenue	188	178
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	740	697
MIS
Disaggregation of Revenue [Line Items]
Revenue	733	827
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	356	417
MIS | Corporate Finance (CFG) | Investment-grade
Disaggregation of Revenue [Line Items]
Revenue	115	114
MIS | Corporate Finance (CFG) | High-yield
Disaggregation of Revenue [Line Items]
Revenue	32	39
MIS | Corporate Finance (CFG) | Bank loans
Disaggregation of Revenue [Line Items]
Revenue	59	113
MIS | Corporate Finance (CFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	150	151
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	99	144
MIS | Structured Finance (SFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	1	0
MIS | Structured Finance (SFG) | Asset-backed securities
Disaggregation of Revenue [Line Items]
Revenue	27	32
MIS | Structured Finance (SFG) | RMBS
Disaggregation of Revenue [Line Items]
Revenue	25	35
MIS | Structured Finance (SFG) | CMBS
Disaggregation of Revenue [Line Items]
Revenue	14	38
MIS | Structured Finance (SFG) | Structured credit
Disaggregation of Revenue [Line Items]
Revenue	32	39
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	142	131
MIS | Financial Institutions (FIG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	3	3
MIS | Financial Institutions (FIG) | Banking
Disaggregation of Revenue [Line Items]
Revenue	100	89
MIS | Financial Institutions (FIG) | Insurance
Disaggregation of Revenue [Line Items]
Revenue	33	34
MIS | Financial Institutions (FIG) | Managed investments
Disaggregation of Revenue [Line Items]
Revenue	6	5
MIS | Public, Project and Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	129	123
MIS | Public, Project and Infrastructure Finance (PPIF) | Public finance / sovereign
Disaggregation of Revenue [Line Items]
Revenue	52	58
MIS | Public, Project and Infrastructure Finance (PPIF) | Project and infrastructure
Disaggregation of Revenue [Line Items]
Revenue	77	65
MIS | Total ratings revenue
Disaggregation of Revenue [Line Items]
Revenue	726	815
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	7	12
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	$ 778	$ 870