Revenues - Revenues Disaggregated by Line of Business and Geographical Area (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
United States
Disaggregation of Revenue [Line Items]
Revenue	768	668	2,320	2,214
Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	704	607	2,116	1,964
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 | United States
Disaggregation of Revenue [Line Items]
Revenue	340	306	991	913
MA | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	340	306	991	913
MA | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	436	379	1,269	1,142
MA | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	436	379	1,269	1,142
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) | United States
Disaggregation of Revenue [Line Items]
Revenue	147	123
MA | Decision Solutions (DS) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			426	376
MA | Decision Solutions (DS) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	207	185
MA | Decision Solutions (DS) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			596	540
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 | Research and Insights (R&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	124	120
MA | Research and Insights (R&I) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			361	352
MA | Research and Insights (R&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	98	81
MA | Research and Insights (R&I) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			293	255
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
MA | Data and Information (D&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	69	63
MA | Data and Information (D&I) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			204	185
MA | Data and Information (D&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	131	113
MA | Data and Information (D&I) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			380	347
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 | United States
Disaggregation of Revenue [Line Items]
Revenue	428	362	1,329	1,301
MIS | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	428	362	1,329	1,301
MIS | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	268	228	847	822
MIS | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	268	228	847	822
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) | United States
Disaggregation of Revenue [Line Items]
Revenue	242	188
MIS | Corporate Finance (CFG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			727	673
MIS | Corporate Finance (CFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	104	89
MIS | Corporate Finance (CFG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			340	343
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) | United States
Disaggregation of Revenue [Line Items]
Revenue	65	69
MIS | Structured Finance (SFG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			186	249
MIS | Structured Finance (SFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	37	32
MIS | Structured Finance (SFG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			117	119
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) | United States
Disaggregation of Revenue [Line Items]
Revenue	52	47
MIS | Financial Institutions (FIG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			188	165
MIS | Financial Institutions (FIG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	74	62
MIS | Financial Institutions (FIG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			225	203
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) | United States
Disaggregation of Revenue [Line Items]
Revenue	69	57
MIS | Public, Project and Infrastructure Finance (PPIF) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			228	210
MIS | Public, Project and Infrastructure Finance (PPIF) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	46	35
MIS | Public, Project and Infrastructure Finance (PPIF) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			143	127
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 | Total ratings revenue | United States
Disaggregation of Revenue [Line Items]
Revenue	428	361
MIS | Total ratings revenue | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			1,329	1,297
MIS | Total ratings revenue | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	261	218
MIS | Total ratings revenue | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			825	792
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
MIS | MIS Other | United States
Disaggregation of Revenue [Line Items]
Revenue	0	1
MIS | MIS Other | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			0	4
MIS | MIS Other | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	$ 7	$ 10
MIS | MIS Other | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			$ 22	$ 30