Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 6,218	$ 5,371	$ 4,829
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(172)	(155)	(143)
MIS
Disaggregation of Revenue [Line Items]
Revenue	3,812	3,292	2,875
MIS | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	165	148	134
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3,977	3,440	3,009
MIS | Corporate finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	2,087	1,857	1,497
MIS | Corporate finance (CFG) | Investment-grade
Disaggregation of Revenue [Line Items]
Revenue	439	636	379
MIS | Corporate finance (CFG) | High-yield
Disaggregation of Revenue [Line Items]
Revenue	411	352	258
MIS | Corporate finance (CFG) | Bank loans
Disaggregation of Revenue [Line Items]
Revenue	606	287	313
MIS | Corporate finance (CFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	631	582	547
MIS | Financial institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	602	530	476
MIS | Financial institutions (FIG) | Banking
Disaggregation of Revenue [Line Items]
Revenue	411	355	320
MIS | Financial institutions (FIG) | Insurance
Disaggregation of Revenue [Line Items]
Revenue	145	137	119
MIS | Financial institutions (FIG) | Managed investments
Disaggregation of Revenue [Line Items]
Revenue	36	28	25
MIS | Financial institutions (FIG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	10	10	12
MIS | Public, project and infrastructure finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	521	496	446
MIS | Public, project and infrastructure finance (PPIF) | Public finance / sovereign
Disaggregation of Revenue [Line Items]
Revenue	244	250	222
MIS | Public, project and infrastructure finance (PPIF) | Project and infrastructure
Disaggregation of Revenue [Line Items]
Revenue	277	246	224
MIS | Structured finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	560	362	427
MIS | Structured finance (SFG) | Other accounts
Disaggregation of Revenue [Line Items]
Revenue	2	2	4
MIS | Structured finance (SFG) | Asset-backed securities
Disaggregation of Revenue [Line Items]
Revenue	118	98	99
MIS | Structured finance (SFG) | RMBS
Disaggregation of Revenue [Line Items]
Revenue	123	96	95
MIS | Structured finance (SFG) | CMBS
Disaggregation of Revenue [Line Items]
Revenue	102	61	81
MIS | Structured finance (SFG) | Structured credit
Disaggregation of Revenue [Line Items]
Revenue	215	105	148
MIS | Rating Revenue
Disaggregation of Revenue [Line Items]
Revenue	3,770	3,245	2,846
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	42	47	29
MA
Disaggregation of Revenue [Line Items]
Revenue	2,406	2,079	1,954
MA | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	7	7	9
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	2,413	2,086	1,963
MA | Research, data and analytics (RD&A)
Disaggregation of Revenue [Line Items]
Revenue	1,745	1,514	1,273
MA | Enterprise risk solutions (ERS)
Disaggregation of Revenue [Line Items]
Revenue	661	565	522
MA | Professional Services
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 159