Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,813	$ 1,472	$ 5,416	$ 4,436
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(51)	(50)	(154)	(148)
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(51)	(50)	(154)	(148)
MA
Disaggregation of Revenue [Line Items]
Revenue	831	776	2,432	2,260
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	834	779	2,442	2,270
MA | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	3	3	10	10
MA | Decision Solutions (DS)
Disaggregation of Revenue [Line Items]
Revenue	383	354
MA | Decision Solutions (DS) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	383	354	1,114	1,022
MA | Decision Solutions (DS) | DS Banking Product and Service | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	140	136	405	390
MA | Decision Solutions (DS) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	148	138	439	404
MA | Decision Solutions (DS) | KYC | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	95	80	270	228
MA | Research and Insights (R&I)
Disaggregation of Revenue [Line Items]
Revenue	235	222
MA | Research and Insights (R&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	235	222	683	654
MA | Data and Information (D&I)
Disaggregation of Revenue [Line Items]
Revenue	213	200
MA | Data and Information (D&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	213	200	635	584
MIS
Disaggregation of Revenue [Line Items]
Revenue	982	696	2,984	2,176
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,030	743	3,128	2,314
MIS | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	48	47	144	138
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	515	346
MIS | Corporate Finance (CFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	515	346	1,569	1,067
MIS | Corporate Finance (CFG) | Investment-grade | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	149	63	416	272
MIS | Corporate Finance (CFG) | High-yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	80	38	232	116
MIS | Corporate Finance (CFG) | Bank loans | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	120	82	422	209
MIS | Corporate Finance (CFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	166	163	499	470
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	135	102
MIS | Structured Finance (SFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	135	102	380	303
MIS | Structured Finance (SFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1	1	2	2
MIS | Structured Finance (SFG) | Asset-backed securities | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	34	30	101	89
MIS | Structured Finance (SFG) | RMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	24	22	73	72
MIS | Structured Finance (SFG) | CMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	27	17	66	45
MIS | Structured Finance (SFG) | Structured credit | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	49	32	138	95
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	170	126
MIS | Financial Institutions (FIG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	170	126	560	413
MIS | Financial Institutions (FIG) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	46	24	166	92
MIS | Financial Institutions (FIG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3	3	10	9
MIS | Financial Institutions (FIG) | Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	108	92	344	289
MIS | Financial Institutions (FIG) | Managed investments | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	13	7	40	23
MIS | Public, Project and Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	154	115
MIS | Public, Project and Infrastructure Finance (PPIF) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	154	115	449	371
MIS | Public, Project and Infrastructure Finance (PPIF) | Public finance / sovereign | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	61	49	187	155
MIS | Public, Project and Infrastructure Finance (PPIF) | Project and infrastructure | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	93	66	262	216
MIS | Total ratings revenue
Disaggregation of Revenue [Line Items]
Revenue	974	689
MIS | Total ratings revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	974	689	2,958	2,154
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	8	7
MIS | MIS Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	$ 8	$ 7	$ 26	$ 22