Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	$ 1,553	$ 1,435	$ 3,153	$ 2,725
Total Expenses	752	725	1,499	1,423
Operating income	801	710	1,654	1,302
Depreciation and amortization	60	58	119	107
Restructuring	0	(2)	2	(3)
Loss pursuant to the divestiture of MAKS	0	0	0	9
Adjusted Operating Income	861	766	1,775	1,415
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	(44)	(37)	(86)	(76)
Total Expenses	(44)	(37)	(86)	(76)
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	980	938	2,016	1,732
MIS | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	1,022	973	2,098	1,804
Total Expenses	362	369	728	712
Operating income	660	604	1,370	1,092
Depreciation and amortization	18	19	36	35
Restructuring	0	0	0	(1)
Loss pursuant to the divestiture of MAKS			0	0
Adjusted Operating Income	678	623	1,406	1,126
MA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	573	497	1,137	993
MA | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	575	499	1,141	997
Total Expenses	434	393	857	787
Operating income	141	106	284	210
Depreciation and amortization	42	39	83	72
Restructuring	0	(2)	2	(2)
Loss pursuant to the divestiture of MAKS			0	9
Adjusted Operating Income	$ 183	$ 143	$ 369	$ 289