Revenues - Revenues Disaggregated by Line of Business and Geographical Area (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,817	$ 1,494	$ 3,603	$ 2,964
United States
Disaggregation of Revenue [Line Items]
Revenue	974	775	1,943	1,538
Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	843	719	1,660	1,426
MA
Disaggregation of Revenue [Line Items]
Revenue	802	747	1,601	1,484
MA | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	806	751	1,608	1,491
MA | United States
Disaggregation of Revenue [Line Items]
Revenue	338	320	675	637
MA | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	338	320	675	637
MA | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	464	427	926	847
MA | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	464	427	926	847
MA | Decision Solutions (DS)
Disaggregation of Revenue [Line Items]
Revenue	366	334
MA | Decision Solutions (DS) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	366	334	731	668
MA | Decision Solutions (DS) | United States
Disaggregation of Revenue [Line Items]
Revenue	138	133
MA | Decision Solutions (DS) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			276	265
MA | Decision Solutions (DS) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	228	201
MA | Decision Solutions (DS) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			455	403
MA | Research and Insights (R&I)
Disaggregation of Revenue [Line Items]
Revenue	226	217
MA | Research and Insights (R&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	226	217	448	432
MA | Research and Insights (R&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	124	119
MA | Research and Insights (R&I) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			246	237
MA | Research and Insights (R&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	102	98
MA | Research and Insights (R&I) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			202	195
MA | Data and Information (D&I)
Disaggregation of Revenue [Line Items]
Revenue	210	196
MA | Data and Information (D&I) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	210	196	422	384
MA | Data and Information (D&I) | United States
Disaggregation of Revenue [Line Items]
Revenue	76	68
MA | Data and Information (D&I) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			153	135
MA | Data and Information (D&I) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	134	128
MA | Data and Information (D&I) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			269	249
MIS
Disaggregation of Revenue [Line Items]
Revenue	1,015	747	2,002	1,480
MIS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,064	793	2,098	1,571
MIS | United States
Disaggregation of Revenue [Line Items]
Revenue	636	455	1,268	901
MIS | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	636	455	1,268	901
MIS | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	379	292	734	579
MIS | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	379	292	734	579
MIS | Corporate Finance (CFG)
Disaggregation of Revenue [Line Items]
Revenue	525	365
MIS | Corporate Finance (CFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	525	365	1,054	721
MIS | Corporate Finance (CFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	342	239
MIS | Corporate Finance (CFG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			714	485
MIS | Corporate Finance (CFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	183	126
MIS | Corporate Finance (CFG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			340	236
MIS | Structured Finance (SFG)
Disaggregation of Revenue [Line Items]
Revenue	131	102
MIS | Structured Finance (SFG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	131	102	245	201
MIS | Structured Finance (SFG) | United States
Disaggregation of Revenue [Line Items]
Revenue	92	60
MIS | Structured Finance (SFG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			168	121
MIS | Structured Finance (SFG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	39	42
MIS | Structured Finance (SFG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			77	80
MIS | Financial Institutions (FIG)
Disaggregation of Revenue [Line Items]
Revenue	195	145
MIS | Financial Institutions (FIG) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	195	145	390	287
MIS | Financial Institutions (FIG) | United States
Disaggregation of Revenue [Line Items]
Revenue	104	73
MIS | Financial Institutions (FIG) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			202	136
MIS | Financial Institutions (FIG) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	91	72
MIS | Financial Institutions (FIG) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			188	151
MIS | Public, Project and Infrastructure Finance (PPIF)
Disaggregation of Revenue [Line Items]
Revenue	154	127
MIS | Public, Project and Infrastructure Finance (PPIF) | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	154	127	295	256
MIS | Public, Project and Infrastructure Finance (PPIF) | United States
Disaggregation of Revenue [Line Items]
Revenue	98	83
MIS | Public, Project and Infrastructure Finance (PPIF) | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			184	159
MIS | Public, Project and Infrastructure Finance (PPIF) | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	56	44
MIS | Public, Project and Infrastructure Finance (PPIF) | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			111	97
MIS | Total ratings revenue
Disaggregation of Revenue [Line Items]
Revenue	1,005	739
MIS | Total ratings revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,005	739	1,984	1,465
MIS | Total ratings revenue | United States
Disaggregation of Revenue [Line Items]
Revenue	636	455
MIS | Total ratings revenue | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			1,268	901
MIS | Total ratings revenue | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	369	284
MIS | Total ratings revenue | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			716	564
MIS | MIS Other
Disaggregation of Revenue [Line Items]
Revenue	10	8
MIS | MIS Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	10	8	18	15
MIS | MIS Other | United States
Disaggregation of Revenue [Line Items]
Revenue	0	0
MIS | MIS Other | United States | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			0	0
MIS | MIS Other | Non-U.S.
Disaggregation of Revenue [Line Items]
Revenue	$ 10	$ 8
MIS | MIS Other | Non-U.S. | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue			$ 18	$ 15