Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 1,522	$ 1,600
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(45)	(42)
MIS
Disaggregation of Revenue [Line Items]
Revenue	827	1,036
MIS | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	43	40
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	870	1,076
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	417	605
MIS | Corporate Finance (CFG) | Investment-grade
Disaggregation of Revenue [Line Items]
Revenue	114	134
MIS | Corporate Finance (CFG) | High-yield
Disaggregation of Revenue [Line Items]
Revenue	39	141
MIS | Corporate Finance (CFG) | Bank loans
Disaggregation of Revenue [Line Items]
Revenue	113	180
MIS | Corporate Finance (CFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	151	150
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	144	116
MIS | Structured Finance (SFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	0	1
MIS | Structured Finance (SFG) | Asset-backed securities
Disaggregation of Revenue [Line Items]
Revenue	32	26
MIS | Structured Finance (SFG) | RMBS
Disaggregation of Revenue [Line Items]
Revenue	35	27
MIS | Structured Finance (SFG) | CMBS
Disaggregation of Revenue [Line Items]
Revenue	38	24
MIS | Structured Finance (SFG) | Structured credit
Disaggregation of Revenue [Line Items]
Revenue	39	38
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	131	162
MIS | Financial Institutions (FIG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	3	2
MIS | Financial Institutions (FIG) | Banking
Disaggregation of Revenue [Line Items]
Revenue	89	109
MIS | Financial Institutions (FIG) | Insurance
Disaggregation of Revenue [Line Items]
Revenue	34	43
MIS | Financial Institutions (FIG) | Managed investments
Disaggregation of Revenue [Line Items]
Revenue	5	8
MIS | Public, Project And Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	123	143
MIS | Public, Project And Infrastructure Finance (PPIF) | Public finance / sovereign
Disaggregation of Revenue [Line Items]
Revenue	58	67
MIS | Public, Project And Infrastructure Finance (PPIF) | Project and infrastructure
Disaggregation of Revenue [Line Items]
Revenue	65	76
MIS | Rating Revenue
Disaggregation of Revenue [Line Items]
Revenue	815	1,026
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	12	10
MA
Disaggregation of Revenue [Line Items]
Revenue	695	564
MA | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	2	2
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	697	566
MA | Decision Solutions
Disaggregation of Revenue [Line Items]
Revenue	334	225
MA | Research and Insights
Disaggregation of Revenue [Line Items]
Revenue	183	171
MA | Data and Information
Disaggregation of Revenue [Line Items]
Revenue	$ 178	$ 168