Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	$ 1,600	$ 1,290
Total Expenses	747	698
Operating income	853	592
Depreciation and amortization	59	49
Restructuring	2	(1)
Loss pursuant to the divestiture of MAKS	0	9
Adjusted Operating Income	914	649
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	(42)	(39)
Total Expenses	(42)	(39)
Operating income	0	0
Depreciation and amortization	0	0
Restructuring	0	0
Loss pursuant to the divestiture of MAKS	0	0
Adjusted Operating Income	0	0
MIS
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	1,036	794
MIS | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	1,076	831
Total Expenses	366	343
Operating income	710	488
Depreciation and amortization	18	16
Restructuring	0	(1)
Loss pursuant to the divestiture of MAKS	0	0
Adjusted Operating Income	728	503
MA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	564	496
MA | Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Revenue	566	498
Total Expenses	423	394
Operating income	143	104
Depreciation and amortization	41	33
Restructuring	2	0
Loss pursuant to the divestiture of MAKS	0	9
Adjusted Operating Income	$ 186	$ 146