Revenues - Consolidated Revenue Information by Geographic Area (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenue	$ 5,371	$ 4,829	$ 4,443
MIS
Segment Reporting Information [Line Items]
Revenue	3,292	2,875	2,712
MA
Segment Reporting Information [Line Items]
Revenue	2,079	1,954	1,731
U.S.
Segment Reporting Information [Line Items]
Revenue	2,955	2,544	2,330
U.S. | MIS
Segment Reporting Information [Line Items]
Revenue	2,068	1,721	1,619
U.S. | MA
Segment Reporting Information [Line Items]
Revenue	887	823	711
EMEA
Segment Reporting Information [Line Items]
Revenue	1,545	1,446	1,377
EMEA | MIS
Segment Reporting Information [Line Items]
Revenue	727	686	669
EMEA | MA
Segment Reporting Information [Line Items]
Revenue	818	760	708
Asia-Pacific
Segment Reporting Information [Line Items]
Revenue	571	551	493
Asia-Pacific | MIS
Segment Reporting Information [Line Items]
Revenue	345	320	300
Asia-Pacific | MA
Segment Reporting Information [Line Items]
Revenue	226	231	193
Americas
Segment Reporting Information [Line Items]
Revenue	300	288	243
Americas | MIS
Segment Reporting Information [Line Items]
Revenue	152	148	124
Americas | MA
Segment Reporting Information [Line Items]
Revenue	148	140	119
Non-U.S.
Segment Reporting Information [Line Items]
Revenue	2,416	2,285	2,113
Non-U.S. | MIS
Segment Reporting Information [Line Items]
Revenue	1,224	1,154	1,093
Non-U.S. | MA
Segment Reporting Information [Line Items]
Revenue	$ 1,192	$ 1,131	$ 1,020