Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	$ 1,435	$ 1,214	$ 2,725	$ 2,356
Total Expense	725	731	1,423	1,411
Operating income	710	483	1,302	945
Restructuring	(2)	53	(3)	59
Depreciation and amortization	58	52	107	102
Acquisition-Related Expenses	0	2	0	3
Loss pursuant to the divestiture of MAKS	0	9	9	9
Adjusted Operating Income	766	599	1,415	1,118
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	(37)	(36)	(76)	(70)
Total Expense	(37)	(36)	(76)	(70)
Operating income	0	0	0	0
Restructuring	0	0	0	0
Depreciation and amortization	0	0	0	0
Acquisition-Related Expenses	0	0	0	0
Loss pursuant to the divestiture of MAKS	0	0	0	0
Adjusted Operating Income	0	0	0	0
MIS
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	938	739	1,732	1,409
MIS | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	973	772	1,804	1,474
Total Expense	369	352	712	688
Operating income	604	420	1,092	786
Restructuring	0	26	(1)	29
Depreciation and amortization	19	18	35	35
Acquisition-Related Expenses	0	0	0	0
Loss pursuant to the divestiture of MAKS	0	0	0	0
Adjusted Operating Income	623	464	1,126	850
MA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	497	475	993	947
MA | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	499	478	997	952
Total Expense	393	415	787	793
Operating income	106	63	210	159
Restructuring	(2)	27	(2)	30
Depreciation and amortization	39	34	72	67
Acquisition-Related Expenses	0	2	0	3
Loss pursuant to the divestiture of MAKS	0	9	9	9
Adjusted Operating Income	$ 143	$ 135	$ 289	$ 268