Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	$ 2,079	$ 1,924
Labor and Related Expense	681	642
Non-Compensation Expense	293	288
Operating, SG&A	974	930
Adjusted Operating Income	1,105	994
Depreciation and amortization	122	113
Restructuring	27	33
Reserve for indirect tax obligations	34	0
Charges related to asset abandonment	0	2
Operating income	922	846
Non-operating (expense) income, net	(52)	(42)
Income before provision for income taxes	870	804
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	(54)	(52)
Intersegment Expense		(52)
Operating, SG&A	(54)	(52)
Adjusted Operating Income	0	0
Depreciation and amortization	0	0
Restructuring	0	0
Reserve for indirect tax obligations	0	0
Charges related to asset abandonment	0	0
MA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	926	859
Labor and Related Expense	374	362
Non-Compensation Expense	202	192
MA | Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	3	3
Intersegment Expense	51	49
MA | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	929	862
Operating, SG&A	627	603
Adjusted Operating Income	302	259
Depreciation and amortization	100	94
Restructuring	20	26
Reserve for indirect tax obligations	34	0
Charges related to asset abandonment	0	2
MIS
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	1,153	1,065
Labor and Related Expense	307	280
Non-Compensation Expense	91	96
MIS | Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	51	49
Intersegment Expense	3	3
MIS | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	1,204	1,114
Operating, SG&A	401	379
Adjusted Operating Income	803	735
Depreciation and amortization	22	19
Restructuring	7	7
Reserve for indirect tax obligations	0	0
Charges related to asset abandonment	$ 0	$ 0