Revenues - Revenue by Category (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 1,472	$ 1,275	$ 4,436	$ 4,178
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(50)	(45)	(148)	(134)
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(50)	(45)	(148)	(134)
MA
Disaggregation of Revenue [Line Items]
Revenue	776	685	2,260	2,055
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	779	687	2,270	2,060
MA | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	3	2	10	5
MA | Decision Solutions (DS)
Disaggregation of Revenue [Line Items]
Revenue	354	308
MA | Decision Solutions (DS) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	354	308	1,022	916
MA | Decision Solutions (DS) | DS Banking Product and Service | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	136	115	390	355
MA | Decision Solutions (DS) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	138	129	404	370
MA | Decision Solutions (DS) | KYC | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	80	64	228	191
MA | Research and Insights (R&I)
Disaggregation of Revenue [Line Items]
Revenue	222	201
MA | Research and Insights (R&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	222	201	654	607
MA | Data and Information (D&I)
Disaggregation of Revenue [Line Items]
Revenue	200	176
MA | Data and Information (D&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	200	176	584	532
MIS
Disaggregation of Revenue [Line Items]
Revenue	696	590	2,176	2,123
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	743	633	2,314	2,252
MIS | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	47	43	138	129
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	346	277
MIS | Corporate Finance (CFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	346	277	1,067	1,016
MIS | Corporate Finance (CFG) | Investment-grade | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	63	67	272	249
MIS | Corporate Finance (CFG) | High-yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	38	21	116	91
MIS | Corporate Finance (CFG) | Bank loans | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	82	47	209	232
MIS | Corporate Finance (CFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	163	142	470	444
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	102	101
MIS | Structured Finance (SFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	102	101	303	368
MIS | Structured Finance (SFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1	0	2	1
MIS | Structured Finance (SFG) | Asset-backed securities | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	30	26	89	89
MIS | Structured Finance (SFG) | RMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	22	22	72	85
MIS | Structured Finance (SFG) | CMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	17	19	45	84
MIS | Structured Finance (SFG) | Structured credit | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	32	34	95	109
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	126	109
MIS | Financial Institutions (FIG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	126	109	413	368
MIS | Financial Institutions (FIG) | Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	92	76	289	258
MIS | Financial Institutions (FIG) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	24	24	92	82
MIS | Financial Institutions (FIG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3	3	9	9
MIS | Financial Institutions (FIG) | Managed investments | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	7	6	23	19
MIS | Public, Project and Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	115	92
MIS | Public, Project and Infrastructure Finance (PPIF) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	115	92	371	337
MIS | Public, Project and Infrastructure Finance (PPIF) | Public finance / sovereign | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	49	44	155	157
MIS | Public, Project and Infrastructure Finance (PPIF) | Project and infrastructure | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	66	48	216	180
MIS | Total ratings revenue
Disaggregation of Revenue [Line Items]
Revenue	689	579
MIS | Total ratings revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	689	579	2,154	2,089
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	7	11
MIS | MIS Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	$ 7	$ 11	$ 22	$ 34