Revenues - Consolidated Revenue Information by Geographic Area (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 1,356	$ 1,240	$ 4,081	$ 3,596
MIS
Segment Reporting Information [Line Items]
Revenue	825	746	2,557	2,155
MA
Segment Reporting Information [Line Items]
Revenue	531	494	1,524	1,441
United States
Segment Reporting Information [Line Items]
Revenue	729	660	2,280	1,910
United States | MIS
Segment Reporting Information [Line Items]
Revenue	506	454	1,625	1,301
United States | MA
Segment Reporting Information [Line Items]
Revenue	223	206	655	609
EMEA
Segment Reporting Information [Line Items]
Revenue	401	362	1,137	1,057
EMEA | MIS
Segment Reporting Information [Line Items]
Revenue	188	175	542	502
EMEA | MA
Segment Reporting Information [Line Items]
Revenue	213	187	595	555
Asia-Pacific
Segment Reporting Information [Line Items]
Revenue	156	142	436	415
Asia-Pacific | MIS
Segment Reporting Information [Line Items]
Revenue	99	78	270	241
Asia-Pacific | MA
Segment Reporting Information [Line Items]
Revenue	57	64	166	174
Americas
Segment Reporting Information [Line Items]
Revenue	70	76	228	214
Americas | MIS
Segment Reporting Information [Line Items]
Revenue	32	39	120	111
Americas | MA
Segment Reporting Information [Line Items]
Revenue	38	37	108	103
Non-U.S.
Segment Reporting Information [Line Items]
Revenue	627	580	1,801	1,686
Non-U.S. | MIS
Segment Reporting Information [Line Items]
Revenue	319	292	932	854
Non-U.S. | MA
Segment Reporting Information [Line Items]
Revenue	$ 308	$ 288	$ 869	$ 832