Revenues - Transaction and Relationship Revenue (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 6,218	$ 5,371	$ 4,829
Percentage of Revenues	100.00%	100.00%	100.00%
MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 3,812	$ 3,292	$ 2,875
Percentage of Revenues	100.00%	100.00%	100.00%
MA
Disaggregation of Revenue [Line Items]
Revenue	$ 2,406	$ 2,079	$ 1,954
Percentage of Revenues	100.00%	100.00%	100.00%
Corporate finance (CFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 2,087	$ 1,857	$ 1,497
Percentage of Revenues	100.00%	100.00%	100.00%
Structured finance (SFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 560	$ 362	$ 427
Percentage of Revenues	100.00%	100.00%	100.00%
Financial institutions (FIG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 602	$ 530	$ 476
Percentage of Revenues	100.00%	100.00%	100.00%
Public, project and infrastructure finance (PPIF) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 521	$ 496	$ 446
Percentage of Revenues	100.00%	100.00%	100.00%
MIS Other | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 42	$ 47	$ 29
Percentage of Revenues	100.00%	100.00%	100.00%
Research, data and analytics (RD&A) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 1,745	$ 1,514	$ 1,273
Percentage of Revenues	100.00%	100.00%	100.00%
Enterprise risk solutions (ERS) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 661	$ 565	$ 522
Percentage of Revenues	100.00%	100.00%	100.00%
Professional Services | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 159
Percentage of Revenues	0.00%	0.00%	100.00%
Transaction Revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 2,810	$ 2,379	$ 2,102
Percentage of Revenues	45.00%	44.00%	44.00%
Transaction Revenue | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 2,640	$ 2,182	$ 1,809
Percentage of Revenues	69.00%	66.00%	63.00%
Transaction Revenue | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 170	$ 197	$ 293
Percentage of Revenues	7.00%	9.00%	15.00%
Transaction Revenue | Corporate finance (CFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 1,600	$ 1,401	$ 1,057
Percentage of Revenues	77.00%	75.00%	71.00%
Transaction Revenue | Structured finance (SFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 362	$ 175	$ 246
Percentage of Revenues	65.00%	48.00%	58.00%
Transaction Revenue | Financial institutions (FIG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 320	$ 265	$ 212
Percentage of Revenues	53.00%	50.00%	45.00%
Transaction Revenue | Public, project and infrastructure finance (PPIF) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 354	$ 337	$ 292
Percentage of Revenues	68.00%	68.00%	65.00%
Transaction Revenue | MIS Other | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 4	$ 4	$ 2
Percentage of Revenues	10.00%	9.00%	7.00%
Transaction Revenue | Research, data and analytics (RD&A) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 91	$ 80	$ 16
Percentage of Revenues	5.00%	5.00%	1.00%
Transaction Revenue | Enterprise risk solutions (ERS) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 79	$ 117	$ 118
Percentage of Revenues	12.00%	21.00%	23.00%
Transaction Revenue | Professional Services | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 159
Percentage of Revenues	0.00%	0.00%	100.00%
Relationship Revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 3,408	$ 2,992	$ 2,727
Percentage of Revenues	55.00%	56.00%	56.00%
Relationship Revenue | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 1,172	$ 1,110	$ 1,066
Percentage of Revenues	31.00%	34.00%	37.00%
Relationship Revenue | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 2,236	$ 1,882	$ 1,661
Percentage of Revenues	93.00%	91.00%	85.00%
Relationship Revenue | Corporate finance (CFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 487	$ 456	$ 440
Percentage of Revenues	23.00%	25.00%	29.00%
Relationship Revenue | Structured finance (SFG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 198	$ 187	$ 181
Percentage of Revenues	35.00%	52.00%	42.00%
Relationship Revenue | Financial institutions (FIG) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 282	$ 265	$ 264
Percentage of Revenues	47.00%	50.00%	55.00%
Relationship Revenue | Public, project and infrastructure finance (PPIF) | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 167	$ 159	$ 154
Percentage of Revenues	32.00%	32.00%	35.00%
Relationship Revenue | MIS Other | MIS
Disaggregation of Revenue [Line Items]
Revenue	$ 38	$ 43	$ 27
Percentage of Revenues	90.00%	91.00%	93.00%
Relationship Revenue | Research, data and analytics (RD&A) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 1,654	$ 1,434	$ 1,257
Percentage of Revenues	95.00%	95.00%	99.00%
Relationship Revenue | Enterprise risk solutions (ERS) | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 582	$ 448	$ 404
Percentage of Revenues	88.00%	79.00%	77.00%
Relationship Revenue | Professional Services | MA
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 0	$ 0
Percentage of Revenues	0.00%	0.00%	0.00%