Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	$ 1,526	$ 1,356	$ 4,679	$ 4,081
Total Expenses	850	714	2,349	2,137
Operating income	676	642	2,330	1,944
Depreciation and amortization	61	56	180	163
Restructuring	0	23	2	20
Loss pursuant to the divestiture of MAKS	0	0	0	9
Adjusted Operating Income	737	721	2,512	2,136
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	(44)	(39)	(130)	(115)
Total Expenses	(44)	(39)	(130)	(115)
Operating income	0	0	0	0
Depreciation and amortization	0	0	0	0
Restructuring	0	0	0	0
Loss pursuant to the divestiture of MAKS			0	0
Adjusted Operating Income	0	0	0	0
MIS
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	925	825	2,941	2,557
MIS | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	967	863	3,065	2,667
Total Expenses	404	339	1,132	1,051
Operating income	563	524	1,933	1,616
Depreciation and amortization	17	17	53	52
Restructuring	0	13	0	12
Loss pursuant to the divestiture of MAKS			0	0
Adjusted Operating Income	580	554	1,986	1,680
MA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	601	531	1,738	1,524
MA | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	603	532	1,744	1,529
Total Expenses	490	414	1,347	1,201
Operating income	113	118	397	328
Depreciation and amortization	44	39	127	111
Restructuring	0	10	2	8
Loss pursuant to the divestiture of MAKS			0	9
Adjusted Operating Income	$ 157	$ 167	$ 526	$ 456