Revenues - Revenue by Category (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
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(53)	(50)	(103)	(98)
Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(53)	(50)	(103)	(98)
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 | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	4	4	7	7
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) | DS Banking Product and Service | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	131	123	265	254
MA | Decision Solutions (DS) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	147	133	291	266
MA | Decision Solutions (DS) | KYC | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	88	78	175	148
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 | 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
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 | Eliminations
Disaggregation of Revenue [Line Items]
Revenue	49	46	96	91
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) | Investment-grade | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	120	94	267	209
MIS | Corporate Finance (CFG) | High-yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	85	46	152	78
MIS | Corporate Finance (CFG) | Bank loans | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	147	68	302	127
MIS | Corporate Finance (CFG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	173	157	333	307
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) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	1	1
MIS | Structured Finance (SFG) | Asset-backed securities | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	34	32	67	59
MIS | Structured Finance (SFG) | RMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	25	25	49	50
MIS | Structured Finance (SFG) | CMBS | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	22	14	39	28
MIS | Structured Finance (SFG) | Structured credit | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	50	31	89	63
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) | Insurance | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	61	35	120	68
MIS | Financial Institutions (FIG) | Other accounts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	4	3	7	6
MIS | Financial Institutions (FIG) | Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	115	97	236	197
MIS | Financial Institutions (FIG) | Managed investments | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	15	10	27	16
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) | Public finance / sovereign | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	67	54	126	106
MIS | Public, Project and Infrastructure Finance (PPIF) | Project and infrastructure | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	87	73	169	150
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 | 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